What is in your RV black tank? Thirteen years after it was made, for one time and one time only, my RV holding tanks are both clean and empty. How did we clean out our RV holding tanks? Why did we clean our RV holding tanks? What was in our RV holding tanks?
Table of Contents
About being helpful
This article has turned into a comprehensive guide to RV sewer systems and is intended to be helpful for RVers and address the task of maintaining their RV holding tanks. While this may seem basic, over the last five years we have improved the way we maintain our RV sewer system. You might consider this as a brain dump about everything about RV holding tanks. I will tell you what we do and what we don’t do.
Knowing how we do this can help you better maintain your RV. Maintaining the holding tanks takes time and routines that increase the likeliness of a well-functioning system. Links in this article are to things we use and like. They are not affiliate links that generate income in any way. The only hope is that you will find this valuable.
Our RV holding tanks are cleaner than has ever been since it was new. I never thought that it could be this clean nor did I realize how much gunk would come out during the cleaning. We had our tanks professionally cleaned. It is a dirty job and I didn’t do it. I didn’t do it because I don’t have the right tools. Later in the article, I will tell you how I might do a better job maintaining my RV sewer system and avoid a professional RV black tank cleaning.
I searched through more than 500 articles on our website and this is the first time I have touched on this delicate subject. It isn’t that I had nothing to say, but rather I didn’t have anything new to say or any reason to say anything that hadn’t been covered before. Now I have some uncommon first-hand knowledge and helpful information to share.
Our filthy RV black tank
The inside of an RV black tank is a filthy place. The inside of an RV grey tank is also filthy. The RV black tank is a holding tank and for us, it is directly under the toilet. So the RV black tank is a place to hold used toilet paper (and the stuff that goes with used toilet paper). The grey tank is the holding tank for our sinks and shower.
We have used our holding tanks every day during our five-year, full-time RV journey. The only exception was in January (2023) when we went on a week-long cruise. The story is here. Spoiled Rotten on Our Cruise
Some RVs don’t have a black tank instead they have composting or cassette toilets. So this article would then apply only to the grey tank. Some really expensive RVs don’t have a separate grey tank instead they have combined black and grey tanks. This article applies to these combination tanks.
The big blue hose is the one we use to rinse our black tank. The white hose on the reel is our fresh water hose. The silver hose in the middle is our hot and cold water hose going to what I call the doggy wash. I use the soap bottle on the left and the spray bottle (hidden on the right) to frequently wash my hands when outside the RV.
RV holding tanks
Notice that I say that an RV black tank is a holding tank. An RV black tank is a temporary holding tank. We dump our tanks about once a week. We can sometimes go more than two weeks before dumping our black and grey tanks. To go without emptying our tanks for two weeks we need to use other toilet and shower facilities. A good example of that was when we were in Key West in January 2022. Our RV was not hooked to any facilities to dump our tanks until we moved the RV. Here is a link to that story. Key West Sunsets and Key West Solar
An RV black tank is NOT a septic tank
The reason that an RV black tank is not a septic tank is that it is only temporary storage. A septic tank is not temporary storage and if properly functioning a septic tank can go years between emptying. The word “septic” refers to the processes that reduce bulk solids and organics
The reason that a septic tank can go years (assuming that input is less than the reduction rate) between emptying is breaking down the contents and reducing its size by a biological process. The best description is that microbes are eating the contents. Liquids in a septic tank are mostly funneled off. Air in a septic tank is restricted (anaerobic) to help the microbes. Both of these things do not apply to a holding tank.
Occasionally, on a septic tank, you need to have a professional pump out the contents. Additionally, you never clean a septic tank, instead, you only empty it leaving the microbes to do their job. The biology that is inside the septic tank would suffer greatly if the septic tank were cleaned. A septic tank is not really similar to an RV black tank except for the contents put into the tank.
RV tank-level sensors are almost always the least expensive sensors that RV manufacturers can install. We have been lucky and have replacement sensors that are better than most RVs, but we also have some issues with our RV tank sensors (more later).
The problem with these sensors is that only after a couple of months of working, they would get coated by gunk in the black and grey tanks and quit working. Later in the article, I will discuss a tank-level system that does work. Unlike many people, we did not clean our RV black tank because the sensors didn’t work.
Why we cleaned our RV holding tanks
Mostly we cleaned our holding tanks because we had time and opportunity. The biggest reason we cleaned our holding tanks was to find out how bad they were. Until you clean your tanks how would you know if they really needed it? It is not like you can see the problem. Even though some RVers never clean their holding tanks we decided that it would be appropriate after thirteen years of use.
You can’t get your RV holding tanks cleaned just anywhere. First, you have to have a water and sewer connection. This eliminates many of the places we stay. So, we had to schedule cleaning at a location where we had a sewer connection.
Not at a dump station
Cleaning the RV black tank takes a couple of hours. Since other campers would want to use a dump station and wouldn’t want to wait a couple of hours, cleaning your RV tanks at a dump station wouldn’t be acceptable.
We also had to be near a professional RV tank cleaner. There are several professional RV tank cleaners scattered across the United States but only a few near where we travel (more later).
How we cleaned out our RV holding tanks
I say “we” here as a collective we, I watched keeping the wind at my back. I paid Joel, a franchise owner from Kleen Tank, to do the cleaning. It is not that I am opposed to doing such a thing myself but frankly I don’t carry the appropriate tools with me in the RV. Sometimes you just have to call a professional.
I will get to the cleaning procedure later (assuming you have a pressure washer) you could clean out your black tank after buying a few specialty tools at a price less than we paid to have our black tank cleaned (more later).
How to care for your RV holding tanks
We have been doing a great job taking care of the RV holding tanks but taking care of and cleaning are two separate things. I say a great job, but that didn’t mean that our RV holding tanks weren’t filthy. To take care of your RV black tank the first thing you want to do is to use plenty of water. This keeps the solids in suspension. Notice how I adaptly avoided using more graphic terms. Suspension means that the solids are floating in the water.
Water in your RV black tank is your best tool to take care of the black tank. Use plenty of water every time you flush the toilet. After you dump your black tank rinse with plenty of water. After dumping I keep rinsing until the water comes out clear.
When you are done emptying the black tank put in plenty of water before you use the toilet to make sure you are not depositing solids from the toilet into a dry empty tank. Keep plenty of water in the toilet bowl when flushing and keep the water contents of your waste flushed down the toilet very high, the more water the better. Solids can lead to problems, and lots of water prevents these problems.
Don’t dump an empty RV black tank
This should seem obvious but to some people, it isn’t. Don’t dump your black tank unless it is more than half full unless you add water to the black tank to aid dumping. Don’t ever let the water out of an RV black tank unless you are dumping it. Never leave your black tank dump valve open and thus allow the liquid contents out of the RV black tank before dumping all the contents.
Dump once, rinse twice
Rinse your black tank frequently, ideally every time you dump the tank. Our RV has a built-in rinse system. The picture of the nozzle is above. Each time that I dump the tank I rinse it multiple times until the water runs clear and all the solids are gone. If your RV does not have a rinse system you can rinse your black tank by introducing water back up through the dump valve and then releasing the rinse water and letting it run clear. Sometimes you may need to rinse more than twice before the water runs clear.
After you close the gate valve, you would open the blue knob on the left side of the picture and allow water from the hose to partially fill the RV black tank. Then after water partially fills the tank you then close the fill valve (blue knob) and open the gate valve.
As I mentioned I have a built-in black tank rinse system and thus the above picture was taken from the Valterra website. Since I have a built-in RV black tank rinse system, I don’t need to use this kind of fitting to flush my black tank. Don’t expect results from squirting water up the dump pipe to equal my built-in flush system. The more water you get into the plumbing and tank the more resistance the water being jetted into the tank will encounter. One of these fittings however would be the only way I can flush my grey tank (more later).
Dump and run
The only exception to a rinse procedure is when I am doing what I call dump and run. This means that I am dumping the contents at an RV dump station before driving to a new destination. At an RV dump station, you probably don’t have time to rinse multiple times. After dumping, then introduce water into the back tank to pre-wet the tank bottom. Introducing clean water into the black tank can be done via the toilet.
After you dump
Each time you dump, after you dump you need to add some water back into the black tank before you use the toilet. I add about five gallons of water to the tank after dumping. If you are going to add chemicals to your tank, this is the time to do it.
Toilet paper only
Don’t ever put anything other than toilet paper (and toilet waste) into your RV black tank. Do not ever put wet wipes or paper towels into your black tank. If you introduce these foreign solids, you run the risk of creating a blockage. Anything other than toilet waste and toilet paper is a big NO. More on this later. Also, look for the title that says “Blockage”. You don’t ever want to deal with a blockage.
Carefully pick your toilet paper. You need toilet paper that will not stay together once wet with water. You want it to fall apart. Small shards of toilet paper are easier to remove than large wads of toilet paper. It doesn’t need to be RV toilet paper but it does need to fall apart once in the water. Some of the most “comfortable” toilet paper brands do not fall apart quickly. We use Angel Soft, from Walmart. It has a low price and quickly dissolves in water.
We purchased this RV (used) from a previous owner. As part of the purchase, we got plenty of RV black Tank treatment chemicals with the RV. In fact, we got so many chemicals that in the last three years, even when frequently using these chemicals we still have plenty. If you don’t own any RV black tank chemicals don’t buy them. I am convinced that these chemicals don’t do anything better than the following soap solution.
Soft water and soap
The only things that you need are soft water and soap. You may have noticed that soft water, especially soft water with soap feels slippery, you want soapy soft water in your RV black tank for this very reason. We have a water softener I built into the RV and thus I only need a few squirts of Dawn dish soap. Ideally, the best dish soap would be liquid dishwasher dish soap. I only recommend using liquid soaps. (I don’t usually recommend things.)
Since we don’t have an automatic dishwasher, we don’t carry dishwasher soap and thus Dawn is good enough. Dishwasher soap almost always has a water softener built in and creates fewer bubbles than sink dish soap. Here is a link to the article about our water softener and water filter. Super-Sized RV Water System
If you have an odor coming from your tanks, then a small amount of Pine-Sol will help control the odor. I have never used Pine-Sol or similar items in my black tank. You need to be certain that you have an odor coming from your black tank, meaning that it is coming up out of your toilet when you flush. Grey tank odor in an RV is much more common than odor from an RV black tank. RV Grey tanks can smell just as bad or worse than the smell associated with your RV black tank. I will discuss this later also.
If you desire you can put some bleach into your black tank (personally, I think that it is a waste of bleach). My RV black tank is 45 gallons (when full) and it is very unlikely that I could put enough bleach into my black tank to hurt any of the components. Experts that I know don’t recommend bleach and consider it as just something that makes some people feel better (like other RV tank chemicals).
Don’t listen to anyone who is worried that bleach will kill the bacteria that live in your black tank. These people mistakenly think that their RV holding tank is a septic tank. In your black tank, you don’t want to hold the contents long enough to start the septic process. Keep bleach out of your septic tank. In the last five years, I have tried chemicals intended to start the septic process and don’t recommend them.
What was in our RV holding tanks
First, in our RV black tank, there was toilet paper and other toilet solids that had not been removed when we last dumped our black tank. This was even though I had dumped it and rinsed it earlier that morning. I was disappointed, but the clear RV sewer fittings showed clearly that my rinse system wasn’t getting all the solids out of the black tank each time I dumped the tanks.
Struvite was in my black tank and is probably in your black tank. Struvite was once thought to be a new mineral, but it is actually magnesium ammonium phosphate. Struvite is a crystallized form of urine. People create struvite in their bodies. When struvite is inside the body it is known as kidney stones. If you have ever met anyone who had kidney stones then you know about the pain associated with struvite.
If you can, you want to avoid struvite collecting on the surfaces inside your RV black tank. The possibility of struvite was one of the reasons we opted to get a professional RV black tank cleaning. You just don’t know unless you check. The pressure associated with a professional RV black tank cleaning will blast struvite off the inside of the black tank surfaces. I was glad that we didn’t have a large buildup of struvite in our black tank. It means that we didn’t really need cleaning, but like a colonoscopy, unless you check, you don’t know what you will find.
Calcium and magnesium
We didn’t see it, but I know that we had some calcium and magnesium inside our tanks. Calcium and magnesium is the white chalky mineral you usually will see on your shower head. This comes from camping in the western states known for hard water. Calcium and magnesium are both in your water heater and in your RV holding tanks. Calcium and magnesium are the white pellets that come out of your water heater when you clean it. You clean out your water heater — don’t you?
Calcium and magnesium are one of the reasons we have a water softener in our RV. A water softener doesn’t completely eliminate calcium and magnesium, but it helps a lot. Really the way to completely avoid this build-up is to only camp at locations with soft water. Our RV black tank cleaning probably didn’t remove any stuck-on deposits of calcium and magnesium. To remove calcium from your shower head, soak it in vinegar.
I wasn’t too surprised that mold came out of our grey tank during cleaning. Mold grows in moist environments. The professional tank cleaning process does a good job of removing mold.
How to clean your RV holding tanks
Choose an RV campsite with a dump station, then call Joel.
Kleen Tank (link below), will do the job for a fee. This will involve putting a stream of pressurized water from a pressure washer into the tank through a specially designed fitting. All the contents that the pressure washer displaces will then run out of the sewer hose and down the drain.
How to clean your RV black tank yourself
I am willing to bet that the pressure washer used by Kleen Tank puts out a lot more water than the typical home improvement store pressure washer. This may be a reason that you may need a professional.
If you have a pressure washer and are willing to spend a little money on some specialty tools you could clean the tank yourself. You could attempt to clean your RV black tank without a pressure washer using an item similar to the Valterra Clog Killler snaked into the holding tanks via the sewer hose. If you do it frequently (about every six months or so) it will keep your black and grey tank pretty clean. Don’t expect the results to equal a pressure washer-based cleaning.
Other than rags and some catch buckets that will be necessary to catch some dripping water (sewer water) the number one thing you will need if you want to do this with your pressure washer is a hydro-jet attachment. This device is sent up into the holding tank and the pressure washer sprays lots of water into the tank flushing the contents out of the sewer hose and down the drain.
If you have a pressure washer and are going to try this yourself here is a link to an Amazon link to product that may do the job. Pressure Washer Sewer Cleaning Kit
The procedure is simple; snake the hydro-jet up into the tank and blast the insides until nothing but clear water comes out. The only tricky part is to catch all the contents into the sewer drain. After you think it is clean then rinse the tank like you normally would after dumping the tank.
The top-down method
Professional RV tank cleaners use the bottom-up method I have been describing. This means they never have to enter the RV and everything is done by inserting the pressure washer tube into the sewer hose via a specially modified fitting.
If you want you can buy or make a cleaning wand and clean your RV black tank by running a hose into your RV and inserting the cleaning wand into the black tank through an open toilet valve. If you do this be careful not to damage the toilet valve seal. Another issue with the top-down method is that you probably are going to get some undesired odor in your bathroom. A limitation of the top-down method is that even though I could clean my black tank using this method it does nothing for the grey tank.
Other things to know about RV holding tanks
To maintain the health of your fresh water tank you should first filter all the water that you put into the tank. All the water we have ever put into our RV fresh water tank passed through our filter and water softener. At a minimum keep filling the fresh water tank with city water (which contains chlorine to kill the bugs) and keep replacing the water in your freshwater tank with new chlorinated fresh water. We use the system described in this post. Super-Sized RV Water System
The water in your grey tank is filthy. Both your black and grey tanks have a vent through the roof of your RV. Make sure that these vents don’t get obstructed. The purpose of these vents is to allow the foul odor from these tanks to escape through the vent. While it is a very, very bad idea to leave your black tank dump valve open, it is fine to leave your grey tank valve open draining into the sewer. It won’t hurt anything.
Our grey tank does not have a flush system so we can’t rinse the grey tank. So to rinse our grey tank we would need a hose attachment similar to the Valterra clog buster.
You don’t need to add extra soap to your grey tank. Your grey tank gets plenty of soap from washing your dishes and your shower. My evaluation is that when we cleaned our tanks our grey tank was worse than our black tank even though it didn’t take as long to clean. The reason the grey tank was worse is that it had never been flushed. Since struvite is a product of deposits you make in your toilet, you will not have struvite in your grey tank.
Each sink in your RV also has what is called a cheater vent. The purpose of this vent is to make your sink drain faster. In a standard house, you will have similar vents that go through the roof. Cheater vents are rare in houses. The problem with these vents is that they can break and allow the smell from your grey tank to enter the bathroom or kitchen. You will swear that you can smell the black tank, but the problem is actually the grey tank and a cheater vent. In my RV, I removed the cheater vent from the bathroom and since I didn’t have a problem with the sink draining I never replaced it.
Under every sink in your RV, you also have a P-trap. When there is water in the P-trap it blocks the grey tank odor from coming back up through the sink. To keep it working pour about a cup of water into the sink and do not let this water evaporate. If you put your RV in storage a few drops of food-grade vegetable oil mixed into this water will prolong the water life. The way this works is that the oil will float to the top of the water preventing evaporation. We don’t have this problem because we use our sinks every day.
Under our shower, we don’t have a P-trap even though most houses do. Instead, we have what is called a Hepvo valve. To clean it we occasionally dump boiling water down the shower drain. Here is a link to the company that makes this valve. Hepvo
RV black tank and toilet
If you get an odor coming out of your black tank (assuming your toilet bowl is clean and holds water), your problem is usually that the vent pipe leading from the black tank through the roof is obstructed. Like the grey tank, the purpose of this vent is to allow air out of the black tank to escape when you put water into the tank. If air instead enters your bathroom while flushing the toilet your black tank roof vent may be obstructed.
Another place where odors can come from is an improperly installed pipe connection to the black or grey tanks, above the water line. Thankfully you won’t get a wet mess but you still really have a big problem. If you are fighting long-term odor this may be your problem. I don’t have this problem and I am very thankful.
We only have one toilet in our RV. If your RV has more than one toilet, then you either have separate black tanks (very uncommon) or you have an electric pump to transfer the toilet contents from the remote toilet to the black tank. I never wanted to repair one of these pumps and this is one reason I only have one toilet sitting directly over the black tank.
The sewer hose (with the lime green fittings) is the Thetford Titan Sewer Hose. We have both a fifteen-foot hose and a ten-foot hose. We also have a hose similar to the small brown hose also in the above photos. We almost always use the fifteen-foot hose and rarely use the ten-foot hose unless we just can’t reach the campground sewer any other way.
The reason I got the Thetford sewer hose was I wanted to have a sewer hose that was as robust as possible. Our sewer hose is now five years old and starting to show wear however it is still the only sewer hose that I have seen and trust. The advertisement says you could step on the hose and not create a leak. I will tell you that I have stepped on my hose, or at least someone stepped on my hose and it does show the deformity but as advertised, it doesn’t leak.
Tank level sensors
I mentioned earlier that our RV is now operating on its second set of level sensors. The first set of sensors was junk. As pictured earlier, a previous owner clipped the wires and they are no longer being used. We now have the SeeLevel II tank monitor. It has mostly been foolproof. Occasionally we will get an incorrect reading, but then without any action on my part, the incorrect reading clears. I wonder if it is working today.
The picture below is the sensor for the SeeLevel II monitor. This one is glued to my grey tank. The way this one works (and continues to work) is these small circuit boards measure the fluid level by density readings. Air in the tank is compared to the fluid in the tank reported to the SeaLevel II tank monitor display.
You NEVER want a blockage
If for some reason you are unable to dump your tanks, it is nearly certain that you have a blockage by some foreign object (children’s toys are a typical cause) and a combination of toilet paper or other paper products. In this case, you are going to have to clear the blockage from the bottom.
Introducing water via the previously pictured Valterra 45-degree hydro flush valve may be able to dislodge the object. If not, you are going to have to come into the sewer line from the bottom with a flexible tube that will jet the object out of the way and clear the object. A cleaning tool similar to the Valterra Clog Killer will be necessary. Quite a few RVers call a professional RV tank cleaner if this happens. Professional RV tank cleaners can fix this. Most plumbers will not have the required tools.
Of course, if this works, when you do this you are only going to get some instant but temporary relief. The object is still in your black tank and will most certainly go back to the place it caused the problem. To remove it you will probably have to remove the toilet and fish it out through the open hole in the top of the black tank. Maybe this would be a great reason to call a professional.
To finish up, I would like to invite you to watch a video by my friend Dave Tigner. I glossed over the procedure of dumping our tanks. Dave does a good job explaining this procedure. If you combine this video with the other details presented above you will have all the information you could ever need.
Step-by-step instructions for hooking up and dumping your RV holding tanks
To seasoned RVers, I probably don’t have anything to add other than a few hints and perhaps an order change to the sequence.
- Put on disposable gloves before
- Remove the cap to the campground sewer pipe
- Remove the cap from the campground end of the sewer hose and attach the clear 90-degree elbow to the end of the sewer hose.
- Always attach the sewer pipe end of the pipe to the sewer before attaching the sewer hose to the RV.
- Attach the end of the sewer hose 90-degree elbow to the campground sewer pipe. Use threaded fittings if available on the campground sewer pipe.
- Place the sewer hose weights across the 90-degree elbow to hold the sewer hose end into the sewer pipe and prevent it from jumping out of the sewer pipe.
- At the RV verify that both the black tank valves and grey tank valves are closed. If the valves are open even a little bit it is a huge problem. If you are not wearing gloves you better put them on now and not proceed any further without gloves.
- If the valves are open, even a small amount then you will have a large accumulation of fluid behind the cap. Remove the cap very slowly to allow the water to trickle into the awaiting sewer hose before you fully remove the cap. Expect this to be disgusting.
- At the RV remove the cap covering the ends of the discharge pipe fitting and the sewer hose. Attach the sewer hose to the RV discharge pipe fitting.
- Support the sewer hose to create a slope leading to the campground sewer pipe.
Dumping and rinsing the holding tanks
- Before releasing the black tank contents allow the grey tank water to fill to mostly full so that you can use the grey water as a final rinse of the sewer hose after dumping the black tank.
- Attach the black tank rinse hose to a water supply to allow rinsing of the black tank. If necessary add water to the black tank using this rinse hose to partially fill the black tank with the black tank dump valve closed before opening the dump valve and releasing the contents.
- Some people suggest dumping a little grey water before dumping the black tank to ensure that the sewer hose is intact all the way to the campground sewer pipe. Black tank contents are a biohazard but grey tank contents are not. If you have a leak you would prefer that it be grey water.
- To dump the black tank, pull the black dump tank valve all the way open. Do not open this valve just a little bit. It should be fully open during dumping. After opening the black tank valve turn on the black tank rinse hose and allow it to run well after the black tank is empty. Most of the solids in the black tank are laying on the bottom and will come out after the majority of the fluid has drained.
- After the water runs clear then close the black tank dump valve and allow some water to accumulate in the black tank and then release it again to rinse out any solids.
- Repeat this rinse as many times as necessary to completely rinse. You are finished when you no longer can see any solids
- After you are finished dumping the black tank, then allow the black tank rinse hose to partially fill the black tank. A few gallons should be added to the tank to pre-wet the bottom of the tank.
- Turn off the water on the black tank rinse hose and disconnect the black tank rinse hose. Allow the water in the rinse hose to discharge on the ground before capping the end and storing the hose.
- Open the grey tank valve and allow the contents of the grey tank to flush the sewer hose.
Disconnecting and storing the sewer hose.
- Always disconnect and cap the sewer hose starting at the RV first. This allows you to lift the sewer hose and drain any remaining water out of the hose into the sewer pipe.
- Store the sewer hose and fittings in a location where if they had any water in the hose that might leak out that it wouldn’t create an issue.
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Our RV holding tanks were cleaned by the Kleen Tank dealer in southern California. I think that Joel and Jennifer did a good job for me. Other than being a customer I don’t have any affiliation with Kleen Tanks.
Joel & Jennifer Hagan • Long Beach, California, email is: email@example.com