Does An RV Black Tank Have An Overflow?

RVs take many forms and sizes, but one thing that they all have in common is a black tank, if they have a toilet installed. But, does an RV black tank have an overflow?

The reason the tank is black is common in all RVs is because it stores human waste from the toilet. 

An RV black tank is a holding tank that holds the wastewater from the toilet, until it is emptied and discarded. 

An RV black tank does not have an overflow. It can continue to hold wastewater until it reaches capacity, but when it is full there is nowhere for the waste to go.

It is important to know what size your RV’s black tank is, so you will know when it needs emptying. No one likes to be caught off guard with an overflowing RV toilet, so knowing these basics should be essential to any camper.

The article will explore the question of whether or not an RV black tank has an overflow. And how to prevent an overflowing toilet in your RV. you will need to know this essential information before using your RV.

How Do You Know When Your RV Black Tank Is Full?

When owning an RV, it is important to keep an eye on your black water tank. You will need to know when it is full and needs emptying, but how do you know when it’s full?

There are a few ways to figure out if your RV black tank is full:

  • Keep track of the toilet use, know how many flushes your tank will hold and make sure that you don’t go over that number.
  • Use a tank sensor to tell you when it’s full.
  • Look for bubbles when flushing your toilet as a sign it’s full.

For seasoned RVers you will get to know intuitively when your tank needs emptying, it’s a sixth sense that comes with being an RV owner. But, for beginners it can be difficult to know when you should empty your black tank, it’s not a nice job so you don’t want to be doing it more often than needed.

If you know the size of your black water tank, say 20 gallons and you know that your RV toilet uses two quarts (half a gallon) per flush then you can use the toilet about 40 times before the black tank is full.

If math isn’t your thing then luckily most modern RVs and campers have sensors in their holding tanks that will tell you when they are full and need emptying. RVs that were built in the last 10 years should have these sensors as standard. You can also buy and install your own sensors, I’d outsource this job though as it can be messy.

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There is another tell to lookout for to see if your black tank is full – bubbles. If you see bubbles when you are flushing your toilet it could be a sign that your black tank is full and it’s pushing air out to make more room. If you see bubbles when you are flushing your RV toilet it’s time to empty your tank.

Does An RV Black Tank Have An Overflow

Does An RV Black Tank Have An Overflow?

Unfortunately RV black tanks do not have an overflow. If your RV black tank reaches capacity there is nowhere for the waste to go. 

Other holding tanks in your RV will have an overflow, but because of the nature of the black tank (human waste) it’s not safe to have an overflow that will dump the contents into the environment.

This means that you will have to keep a close eye on the levels of your black tank to ensure it doesn’t overflow. Use the methods outlined above to keep your black tank from overflowing.

What Happens If I Overfill My Black Tank?

Now you know that your RV black tank doesn’t have an overflow, you’ll want to know what happens if you forget to empty your tank and the unthinkable happens – you overfill your black tank.

There are a few things that can happen if you overfill your RV black tank:

  • Waste will fill and come out of the roof vent pipe.
  • Waste will come back out of the toilet.
  • Your black tank could burst.

None of these options are good, so make sure that you regularly empty your black tank.

Overflow Via The Roof Vent Pipe

If your black tank is at capacity and you keep adding more waste then the waste will find the path of least resistance to reduce the pressure. One of those paths could be your vent pipe, these typically go to the roof. 

Unfortunately if your waste does decide to take this route out it can take longer to notice and when you do notice – by the smelly human waste coming out onto the roof of your RV.  it’s also a huge clean up job. 

Not only will you have to clean your roof and sides of the RV, your vent pipes will also need thoroughly disinfecting. This isn’t a small job, so make sure that your waste doesn’t have an opportunity to escape via your vent pipes by emptying the black tank.

Overflow Onto The Bathroom Floor

Another route the waste from the black tank can take is back out of the toilet. Luckily (if you want to call it lucky) you will notice this much earlier than if it overflows through the vent pipe.

If the black waste overflows into the bathroom it will be easily noticeable and easy to clean up. Just make sure that there is plenty of ventilation and you use disinfectant when cleaning.

Clean it up immediately to avoid your RV smelling like a sewer for the rest of its life, and also to prevent more serious water damage.

The Black Tank Bursts

If the overflow can’t find a way out through the toilet or vent pipe then the pressure will build in the holding tank and it will eventually burst. 

If the black tank bursts then this will leak raw sewage throughout the undercarriage of your RV. As you can imagine it isn’t a cheap or easy job to clean and repair this, it will spread to every corner as it is liquid and will contaminate everything it comes into contact with.

Not only will you need to buy a new black tank but the repair costs will be very expensive too.

Does An RV Black Tank Have An Overflow?

How long can I leave my RV black tank full?

Many people are unaware of the dangers of leaving an RV black tank full for extended periods of time. The first thing that should be known is that the contents can begin to produce methane gas, which has a narcotic effect on humans. The next thing to keep in mind is that bacteria can quickly build up and release hydrogen sulphide, which is toxic to both animals and humans. Not to mention a full black tank will stink if you leave if full.

Empty your black tank after every camping trip, even if it’s not full and you plan to use it again next week. Plans can change and before you know it your RV has been sitting there for 2 months and the smells have permeated everything inside.

After every camping trip dump your waste and fill the tank with soapy water for the drive home. When you get home, dump the soapy water and you will have a black tank that’s as good as new for your next trip.

How To Avoid RV Wastewater Tank Overflow

Empty all your holding tanks after every trip in your RV, this way you’ll not only reduce the smells from sitting wastewater in your RV but you will know that you are always starting every trip with a blank slate. 

Before your trip check that the sensors in your tank are working properly. Make sure that they are free from blockages and damage as well. Have a check of all the valves and check for any damage like cracks or signs of water.

The more you use your RV the better you will get at sensing how full your tanks are. You will know how many days you can go in your RV before you need to empty the tanks. With this in mind make sure that you plan your trip so you can empty out the tanks when you need to.

Does An RV Black Tank Have An Overflow? – Final Thoughts

Black tanks are possibly the worst bit of RVing, and the last thing you want is for them to be full. RV black tanks don’t have any overflow so if you fill it to capacity the results will be disastrous.

  • Waste will fill and come out of the roof vent pipe.
  • Waste will come back out of the toilet.
  • Your black tank could burst.

Use the tips given in this article to prevent your black tank from overfilling and ruining your holiday (and your RV).

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