What Happens If You Overfill the RV Waste Tank?

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  • Post last modified:November 3, 2019

What Happens If You Overfill the RV Waste Tank?If you are unlucky enough to overfill the “black” tank in your RV here are some of the things that you can expect. These are not the only things that can happen, but an educated selection based on many years of experience and discussions around the world. Also, keep in mind that there is a vast difference between wastewater and “gray” water. Depending on the type of system that is installed on your unit, there are 3 scenarios that typically occur.

  1. The wastewater will fill and travel up the vent pipe.
  2. The wastewater will fill to capacity.
  3. The holding tank for your RV may physically burst.

None of these are ideal, so keep reading as we delve into the details of what can occur in each of these situations, as well as how to avoid them, or clean up if one of them does happen to you!

What Happens if You Overfill the Waste Water Tank?

The Wastewater Will Fill and Travel up the Vent Pipe.

If this happens the waste will expel wherever the vent terminates. This is typically on the roof of the RV or through a side vent typically in the wall. In either case, there will be quite a bit of cleanup required. This typically happens when backflushing an empty tank during cleanout.

The Wastewater Will Fill to Capacity.

Once this has happened the waste will overflow the toilet and expel into the bathroom. This usually happens when there is a good seal between the tank and toilet. This is quite unsanitary and will require a large amount of cleanup. This may also require repairs, and those cost money.

The Holding Tank for Your RV May Physically Burst.

Emptying RV waste tank

Tanks are typically made out of plastics and polymers. If your tank has filled beyond capacity then the materials may give out due to weight and pressure. This will cause the waste to pour into the area that the tank occupies. The waste will also spread anywhere that a liquid can go. This is sure to lead to costly repairs, and maybe an early end to your vacation.

Does an RV Black Tank Have an Overflow?

When thinking about the waste system in your RV there are a few great things to keep in mind. In older models, there is no overflow for the black water.  As technology and design have changed over the years new parts have become available. It will be very clear if you have an overflow, it is usually well marked and located on the underside of the RV very close to the cleanout valves.

Why Does my RV Toilet Bubble When I Flush?

If you notice a bubbling sound when you flush the toilet in your RV check the black water level. This usually happens when the vent pipe is covered by water or waste. While you may be able to get by for a day or so without causing damage, it is recommended that you empty the waste tank and just avoid the possibility of an overflow.

RV Toilet Overflow Cleanup

In the event of an overflow, cleanup will be needed. Depending on the size and location of the overflow this may become difficult. A common trick to making this easier is to use a wet/dry vac to remove as much of the liquid as possible. You may attempt to apply household cleaners or bleach but it is not suggested.

In most cases, the carpeting will need to be cut away and discarded. The underlying floor should be cleaned with a diluted bleach mixture. This will eliminate bacteria and germs. The affected area should then be allowed to air dry.

In some cases, the belly pan of the RV may need to be opened. If this is required, using old clothes and protective gear is recommended. One does not know how much liquid will come out. Cut a section out that is approximately the size of the tank. This will also allow you to locate the source of the overflow and repair it.  It should be noted that cutting a “window” is not suggested as it is actually easier to remove and replace a larger area of the belly pan.

Remove any wet insulation or carpeting.  The area should be allowed to drain fully. Once the repairs have been made, use a bleach and water mixture to thoroughly clean everything. Allow the area to dry and replace the portion that was cut out.

Post Cleanup

Some common post-cleanup suggestions are to coat wooden floors in the affected areas with a clear coat of paint. This will also act as an odor barrier. For the underbelly or damaged compartments, any paint similar to Kilz has been known to work wonders. If the area shows signs of rot or sagging due to prolonged exposure, replace the damaged areas and check the surroundings for further damage.

How to Avoid RV Wastewater Tank Overflow

Emptying RV waste tank after camping

Before heading out in your RV always check your tank levels. Make sure that the sensors are free and clear of blockages. This will make sure that your levels are accurately measured.   It is always best to have a working knowledge of your tanks and how fast they fill with average use.  Have a plan for what to do with your waste.

Check your valves and make sure that they seal properly. Inspect the areas around the tank for cracks, leaks, and signs of wear. Check your toilet seal and the surrounding areas for signs of leaking. Make sure that the vent opening is free and clear of debris.

Proper Planning is Key

Having a black water issue is never fun. The best way to avoid an overflow is to keep an eye on the tank levels. They may add weight to your RV but they can save you the agony and expense of an overflow. At the first sign of trouble, be proactive as this can save you a lot in the long run.  Proper planning, maintenance, and attention to detail are always the best defense against future problems.

New to RV’ing? Check out these 49 RV Maintenance Tips to learn more about how to avoid problems!

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