Does an RV Black Tank Have an Overflow?

Does an RV Black Tank Have an Overflow

RV ownership and rental has some great benefits. But dealing with the black tank is not one of them. If you have ever had to empty a black tank or have one overflow them, you will know what we are talking about.

For those of you out there that are new to this RV life, we are going to answer an important question for you. Knowing whether or not a black tank has an overflow is going to make RVing much easier. 

Does an RV black tank have an overflow? No, an RV black tank does not have an overflow. There is nowhere for the waste to go if the tank is full; that won’t cause an issue.  If your black tank gets too full, there are three things that can happen.

  • The waste can back up the vent pipe and end up on the roof.
  • The waste will end up overflowing onto the bathroom floor. 
  • The black tank will burst (this option is going to be expensive to fix).

While we know that none of this sounds glamorous, it is important to have a clear understanding of the RV waste system.

Knowledge, even too much knowledge, will keep disasters that could have been prevented from happening.

In this article, we are going to talk about what can happen if the black tank overflows and what those things mean for the owner or renter of the RV. 

Where Does Black Tank Overflow Go?

Where the black tank overflow goes when the valves are shut, or the tank is full is not where you want the waste to be.

The only place you want the waste is in the tank or in the place you are allowed to empty the waste. However, even the best-laid plans go astray, and that means there are going to be times the waste ends up on the floor or on the roof. 

rv black tank

Since the waste has to have someplace to go if the tank isn’t cared for properly, there are two options of where it will end up.

Neither one of these options are going to be good.  However, these are the best two alternatives; the other option we will talk about later is definitely the most expensive to fix. 

Related: Is Charmin Toilet Paper safe for RV? – What You Need To Know

Roof Vent

You don’t want what is in your black tank to be hanging out on your roof. Which is what can happen when you have an overfilled black tank.

That is going to be a smelly problem, and it won’t be easy to clean up. But when is waste easy to clean up?

What isn’t a good thing is that the waste is now traveling up your vent pipe straight to the roof. The black smelly goo is now seeping all over your roof. Cleaning this up is going to be a job that you would like to give to someone else.

The tank needs to be emptied; the vent pipes need to be flushed and cleaned, all while the roof needs a good scrubbing. 

This overflow option is likely to be the one that will take the longest to spot. Depending on how many people are using the RV toilet and how many times a day it is flushed, it could take a few days for the waste to travel all the way up the vent pipe. 

Bathroom Floor

A toilet overflowing onto your bathroom floor is a pain in a normal house, but when everyone is living in close quarters, it is much worse.

This is the natural consequence of not taking care of your black tank and emptying it as you should. It is also what happens when the valve is closed. You need to make sure that if a full tank isn’t causing the overflow that the valve is open. 

This is the best possible option when it comes to a black tank overflow. It is the easiest to clean up and doesn’t cause as much damage and also is an easy problem to prevent. 

We flooded our RV – RV Gray Water Tank Overflow >> Check out the video below:

If this happens, you will need to make sure you clean and sanitize well. It is also important to clean it up immediately because it can cause other issues, such as ruining the flooring and seeping under showers, tubs, and doors into the rest of the RV. 

Overflow Alternatives

Now that we have talked about the best-case scenarios when it comes to black tank overflow, we are going to address the worst-case scenario.

Yes, there is a scenario that is worse than hosing toilet waste off of the roof of your RV. It is also a much more expensive option. 

Black Tank Can Burst

When the black tank is full, and the valve is closed, it is a recipe for disaster. An expensive disaster. When the waste has nowhere to go, and you continue to forget to empty it, the pressure continues to build.

If the pressure becomes strong enough, it will burst the black tank. Just think raw sewage bursting forth from under your RV. 

Not only is this smelly and a mess, but it is going to cost to fix it. There isn’t a way to fix a broken black tank. It won’t hold, and you will have a mess again soon. So the entire structure will need to be replaced.

Not only will the tank need to be replaced, but you may be heading home early from vacation. It depends on whether or not you are renting and if you can find someone to fix it close to where you are. 

How to Tell When the Tank is Full

There is a clear sign that your tank is close to being full. As your tank nears the fill line, you will need to pay attention to the toilet when you flush it.

If you have been RVing for a while, then you will have a good idea of how long the tank can go without being emptied. For the new guys, you will need to watch for the signs. 

When all else fails, be cautious and check the fill line or just empty the tank. 

Related reading: Where to Properly Dump Portable Toilet Waste?


You don’t need to be paranoid about checking the tank or staring at the toilet when you flush it, but you do need to be vigilant. One of the best ways to know if the tank is getting full is bubbles.

If the water bubbles as the toilet flushes, then you will need to check the tank. 

The bubbles could also come after you flush the toilet. As the water is filling back up in the toilet bowl, there may be some large bubbles.

It will be like there is air in the tank. What this means is that the tank is overfull, and the waste is pushing out all of the air to make room.

This is a good sign that it needs to be emptied soon. There is a possibility that it just bubbled that one time, but make sure to check the tank anyway. 

Related reading: Is It Safe to Put Bleach in RV Black Tank? (Clean Black Tank in 4 Steps)

Final Thoughts

Going on an RV adventure can be an amazing family getaway. There are some maintenance issues that can’t be ignored. The Black tank is at the top of the list. Nothing will ruin a vacation quite like raw waste overflowing or busting the tank. 

Since the black tank doesn’t have a built-in overflow, it will find a way to overflow that will ruin your day. Make sure you are checking the black tank levels frequently. This will save you a lot of trouble. 

Recommended Reading

You might want to check out our other articles about RV toilets for more information.

Do RV Toilets Have Wax Rings? Here Are The Facts

Can You Flush Tampons Down an RV Toilet? Facts You Should Know

This Is Why Your RV Toilet Foot Pedal is Leaking – [How to Repair]

How Much Water Do You Use In A Shower? (All About Shower Length)

Mike Gilmour

Hi, I'm Mike, co-founder, and editor of RV and Playa. My passion is traveling (with my RV) and enjoying the day at the beach (Playa)! Well, I originally created this blog as a way to share what I've learned by experimenting with the RV lifestyle, and I want to help others develop in life through new skills and opportunities.

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