What To Do When Black Tank Won’t Drain Empty (Helpful Guide)

But it happens more often than you may realize. The black tanks can get stuck from time to time and you need to be prepared for when it happens. There are plenty of sources for this issue and some sources are not as foul-smelling to fix as others.

The first thing to do is check to see if there is a clog in the drain. If there is, you may have to open the gray and black tanks at the same time to create a strong vacuum. That vacuum can push the clog out easily without getting your hands dirty.

To learn more sources and solutions to this problem, just continue to read our article. It has the information you need to know about so you can easily fix this tough situation when it happens to you. Take a few minutes to see how this information can solve your clogged black tank problem.

Why is My Black Water Tank Not Draining?


There are several sources for this problem. To start things off, there are two very simple and easy to fix sources that can make life a little more difficult for you. These take a few minutes to solve.

The first source will be a lack of water in the black tank. Your waste may have formed a nice pyramid inside the black tank and blocked the drain. You can try to break it down with a little soap but that may not always work.

Use some hot water and soap together to see if that removes the pyramid and clears the drain. The second source may be that someone used wipes or extra thick toilet paper when they were finished using the bathroom.

Again, and if this is the case, you can use hot water to clear that clog. The wipes or toilet paper should dissolve in hot water faster and clear the pipes. If you are buying thick toilet paper, it may be a good idea to go to the thinner brand.

The thinner toilet paper should not clog up as easily as thick toilet paper does.

RV Black Tank Won't Drain


Those are the easy sources to fix and there are some other sources that are not so easy to solve. The next source may start during the construction of your RV or trailer. Sometimes the workers cut the plastic area out of the toilet tank and the plastic falls into the drain or tank.

When that happens the plastic part clogs up the drain or the pipes and makes sure that nothing comes out of your black tank. In this case, you would need an RV-safe plumber’s ‘snake’ to get that plastic piece out of the way.

This is a bit messier than other methods but it may be the only one as hot water won’t dissolve plastic. Another possible source is a lot cleaner but it may be harder to fix.

Chances are that at some point some owner will have had the cable come loose from the valve system. They pull on the cable to open the valve and nothing happens. This is indicative of a problem with the valve or the cable.

The cable may have broken or it may have come loose. The set screw could have unscrewed just enough due to the vibration of the RV or trailer while in motion. To solve this you are going to have to find the valve and look at the cable.

If you want, you can let a professional handle this repair. The valve and cable may not be in the easiest to access spot on your RV, etc.

Black Water Tank Not Draining Completely


In this situation, the source of this problem could simply be a lack of water in the tanks. Most owners flush their black water tanks with their gray water tanks. Usually, this works well and helps get everything out of the black water tank.

But on some occasions, there may not be enough water in either tank to thoroughly empty the black water tank. You may have to get your tank cleaning wand out and spray more water into the tanks.

Another solution would be to fill both the gray and black water tanks all the way. Then pull the drains on both at the same time. The suction formed by the gray water tank emptying helped pull the clog out and let the black water tank drain normally.

The key is to pull the valves at the same time or as close to the same time as possible.

What do I do If My Black Water Tank is Clogged?


The first thing to do is to check for the source of the problem. Once you find the source, you can pick the appropriate solution to solve the problem. The source will dictate the solution or method used to clear it.

The second thing to do is not to panic. These problems are not hard to solve and will only take a few minutes if the problem is not serious and in need of a repairman.

Generally, hot water solves a lot of these issues and can have the black tank functioning like normal in no time. Also, you may want to change the type of toilet paper you are using. Go from 2-ply to 1-ply.

Also, you can put a hose to your toilet and run some water down into the black tank and try again. This will help clear out pyramids and clogs as the pressure should push them out or disintegrate them.

Also, if you have young kids or young grandchildren, check the toilet and drain for any flushed items like toys, toothbrushes, and so on. These can clog up a drain or valve and make sure nothing gets out.

How do You Unclog An RV Sewer Tank?


The biggest challenge you will have is the construction materials used to build your black water tank, drains, pipes and toilets. These items are not as tough as the ones found in your home and you cannot use the same tricks to unclog a pipe, etc., as you would at home.

The first thing not to do is use caustic chemicals that open traditional home pipes and toilets, etc. Those caustic products are Drano and bleach. You can use a Calgon water softener mixed with some Dawn liquid soap.

Mix about 1 cup of Dawn with some Calgon and flush it into your black water tank. Then follow that mixture with hot water. When that is done, take your RV or trailer for a drive and let it all slosh around for at least 30 minutes.

Let it sit overnight. Then empty the tank. If you are using any store bought chemical solutions, make sure to follow all instructions to the letter. The next morning, open the valves and drain the tank.

Make sure to use your wand to flush out anything that remains inside the tank. Then close up the valves, put everything away and relax. You may not have this problem again for some time.

How do You Unstick a Black Valve?


This is a common problem as the black tank gets a lot of gunk etc., flushed into it. Eventually, your valve may get stuck and you will have to take care of the problem.

When you have a full black water tank, you need to mix some Dawn liquid soap with some water and pour the mixture into your tank. Then take a drive to slosh it around till your valve gets lubricated.

There is a method you can use that will help you avoid this problem. The key is to do this while your black water tank is emptying like normal. This method is a bit of preventive maintenance.

Most, if not all, RVs and trailers have a rod that controls the opening and closing of the valve. Sometimes this rod gets stuck due to the debris etc., it encounters.

To prevent this from happening, all you need to do is spray some silicon lubricant on the rod when it is open. This keeps the rod in good shape and debris should slide right off.

Do this on a regular basis and you should not have to face a stuck rod or valve again. But since nothing is perfect or guaranteed, you may face it eventually again.

Some Final Words

There are many sources for a black water tank refusing to empty its contents. The best way to find the right solution is to figure out the correct source. Then go from there.

This is not a rare problem and many RV owners face this issue all the time. What you want to avoid when you dump your tank is having any waste remain behind and forming blockades.

Make sure to flush out your tank after each dump to make it truly empty when you are done.

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