RV Grey Tank Not Draining? Why & What To Do

If you’ve been using your RV for a while, or even bought one second-hand, then emptying the holding tanks is probably called for. Specifically, today we’re going to talk about the grey water holding tank, particularly problems with emptying it. So, why is my RV grey tank not draining, and how do I get it to drain? 

There are three major issues that can be causing your grey water tank to not drain. This includes organic blockages, inorganic blockages, and broken components, such as the T-handle or gate valve. You can use hot water, DIY drain cleaning solutions, and you can even use the black tank to empty it too. 

RV grey tank not draining

How Do I Unclog My RV Grey Water Tank? What To Do

There are so many things that could be clogging your RV grey tank and preventing it from draining properly. It’s hard to tell that an RV’s grey tank is clogged until you actually go to empty it. 

Another sign that your grey water tank is clogged is if water starts backing up in the RV’s sinks and showers. That said, there are a number of methods to unclog that RV grey tank, so let’s take a look. 

1. Check The Drain Valve

Before attempting to actually unclog the RV grey tank, you should check the drain valve to see that it is functioning properly. When you turn the handle for the drain valve on the outside of the drain, this would translate to movement on the inside. 

However, if the handle or the drain valve is broken, turning the handle might not cause the valve to open. If this is the case, then you will need to repair the drain valve handle and the valve itself. 

However, this is something that is quite difficult to do. If it is the drain valve handle that is broken, you may require professional assistance. 

That said, if this is not the problem, then you definitely have a clog in your RV grey tank. Generally speaking, it’s much more likely that your RV grey tank is clogged than the handle being broken. Therefore, let’s move on and figure out how to actually unclog an RV grey tank.

2. Unclog It With Hot Water

One of the easiest ways to unclog an RV grey tank is to use a lot of hot water. All you need to do here is to flush out all of the pipes using hot water, as this can help to clear out anything stuck on the inside. 

Here, you are going to boil up to 8 or even 10 gallons of water, realistically, just as much as you can manage at once. 

You are then going to remove any and all strainers, caps, and drain gates from the equation. You now want to pour that hot water into the sink, the shower, and anywhere else possible. The more water you can get in there, the better. 

Pour this into the drains during the evening, and let it sit overnight. If it is still clogged in the morning, you can try repeating the process for a second time. If this still does not work, move on to the next solution to unclog your RV grey tank.

3. Unclog The Grey Tank With Drain Cleaner

If hot water alone did not work, there are also a variety of chemicals that you can use to unclog an RV’s grey tank. There is a variety of unclogging chemicals designed specifically for use with RV’s. These are usually enzymatic drain cleaners. 

This means that they use enzymes and bacteria to eat through clogs. With that being said, these enzymes and bacteria can usually only eat through organic materials, such as hair, grease, human waste, and sometimes even toilet paper. However, they won’t be able to get rid of the inorganic blockage. 

Therefore, we do recommend doing some research on specific RV drain uncloggers. What you do need to know however is that using caustic chemicals absolutely has to be avoided. This means that you absolutely cannot use something like Drano or bleach, as they can damage the tank and the seals are within the tank. 

If you would rather use something a little more natural, you can always try mixing a whole lot of baking soda and vinegar, as that chemical reaction creates a lot of oxygen that may unclog a clogged drain. some people also pour up to three cups of dishwashing liquid down every drain, as this may also do the trick. 

Once you have poured your solution of choice into your drains, take the RV for a bit of a drive so the solution can get all over the grey tank. If by the end of the day this has still not done the trick, move on to the next possible solution.

4. Use A Drain Snake To Unclog The Grey Tank

If none of the above methods worked, it might be the case that you have an inorganic clog in the RV grey tank. If this is the case, you are going to want to get yourself a drain auger, also known as a drain snake. 

Just make sure that you are using a manual drain auger, not a mechanical one, as this could cause damage to the plumbing of your RV. In order to use a drain auger, you first insert the auger into the drain, then you’re going to want to turn the handle clockwise to hook the clog onto the front. 

Once the clog has been hooked onto the front of the drain auger, pull out as much of the debris as you can, and then flush out the drain using hot water. 

If you have an extremely stubborn clog, you can first use an RV drain unclogger, as discussed above, and then follow it up with the snake you may also need to use a flush valve to complete this task.

5. Use The Black Water Tank To Drain The Grey Water Tank

The fact of the matter is that the grey tank does not have a direct outlet like the black tank, and can therefore be a bit of a challenge to enter. Therefore, using the black water tank to access the grey water tank is another solution. That said, make sure that you have completely drained and emptied the black water tank before doing this. 

You don’t want your raw sewage getting into the grey tank. You want to empty your black tank, and then use a black tank spray to clean it. You then also want to use at least five to ten gallons of hot water with dish soap, pour this into the toilet a few times, and flush it. 

You are now going to fill this same tank with fresh water, as this is what you will use to flush out of the great tank. That being said since there is no direct access to the grey tank, getting a lot of water in there at once can be difficult. 

Therefore, you want to get as many people as you can pouring as much water as possible into as many drains as possible at once. Everybody should be pouring several gallons of boiling hot water down the sinks, toilets, and showers. This will allow a lot of water to flow through the pipes at once, hopefully clearing out any debris.

Related: Guide on draining your fresh water tank.

What Happens When Your Grey Water Tank Is Full?

If the grey tank on your RV is full, the water will no longer be able to move down the drains from your shower, sink, and toilet.

Generally speaking, that water is going to back up, and this means that it is going to come out of the drain that is the shortest distance from the grey water tank.

If you see water backing up in the sink or shower closest to the grey water tank, then you know what the issue is.

How Do I Know When My Grey Water Tank Is Full?

As mentioned above, if your grey water tank is full, then the drain closest to that tank is going to back up. You’re going to see water backing up in the sink or a shower. Many modern RV’s may also come with sensors that will tell you exactly when that grey tank is full.

How To Drain Grey Water From An RV

Thankfully, if there are no issues, draining grey water from an RV is very easy. You simply have to connect the sewer hose that matches the drain valve on your RV to that drain valve, and then put that sewer hose into the dump station hole, and then open up the grey water tank valve, and all the waste should easily flow out.

Can I Put Bleach In My Grey Water Tank?

You should absolutely never put any caustic chemicals such as bleach into your grey water tank, as this can cause serious damage to the interior of the tank, the seals, and the gaskets.


You should now know exactly how to drain and unclog the grey water tank in your RV. If nothing else has worked up until this point, then you may need to call a professional for assistance.

Madeline Cooper