Saturday, December 9, 2023


How do I get rid of mold in and around my RV’s toilet?

Dear Dave,
Our RV toilet has been getting a black substance below the water line. When we flush, the water has a black tint to it. Then, within a few hours, the mold-like substance seems to grow on the surface of the flush ball and the china bowl below the water line. It brushes off easily but comes right back. It’s only happening in the toilet, not in any of the sinks or shower. Has anyone else ever heard of such a thing, and how did they get rid of it? —Roger, 2006 Montana 2955RL

Dear Roger,
I believe it is mold, as there is moisture and typically heat in the area you are describing. Mold grows by tiny spores that start invisible and typically float through the air and land on wet surfaces and then start to darken. In your case, the water valve is fresh water coming in to help flush the toilet and there must be a leak or condensation there.

And since it is spreading to the china bowl and flush ball, the spores are in just about every part of the toilet and may even be spreading from inside the tank.

I would start by cleaning the tank with Thetford Tank Blaster. Pour in a pouch and fill the tank or add 50 gallons of water, whichever comes first. Let it sit overnight then dump it.

Bleach or no bleach?

The Environmental Protection Agency recommends not using bleach as it could cause toxic fumes and can harm your respiratory system. I have helped several agencies such as the Red Cross and others during flood cleanup and we have always used bleach with the proper equipment such as rubber gloves, safety glasses, and N95 mask. So, I feel comfortable using it. I suggest using 2 cups of bleach for every 50 gallons of water. Fill the tank again, drive around, let that sit overnight then dump it.

You may want to remove the toilet valve to thoroughly clean it with 1 cup of bleach in a gallon of water. Let it sit in the bucket of solution overnight, as well. Bleach is one of the best products to get rid of mold; however, it is a little smelly and can be an irritant to eyes. Wear rubber gloves and safety glasses when using it.

Clean toilet and surrounding areas

You may want to use the bleach solution to wipe the entire toilet and surrounding areas. Let it sit for 4 hours then wipe it off with a 50/50 solution of ammonia and water. (Do not combine liquid bleach and ammonia.) Spray this on the surface and let it sit for 2 hours before wiping it off.

It may also be necessary to remove the toilet, as mold can hide between the base and the floor and around the seal. If you have carpet on the floor, it might need to be replaced.

If you do not want to use bleach, there are other products on the market that claim to kill and prevent mold without bleach or ammonia. One product is Concrobium Mold Spray, available on Amazon here.

It has a proprietary ingredient. However, the MSDS sheet lists trisodium phosphate, which is TSP and is widely used for cleaning surfaces prior to painting and staining concrete. TSP can be found at any home improvement store.

Some companies recommend other products such as Borax, white vinegar, and even hydrogen peroxide. The main issue is to stop it with the correct cleaner, keep the moisture down, and ventilate. I believe you have just been wiping off what you see and not getting to the root of the problem.

Tips to reduce mold

After cleaning thoroughly, ventilate the area by running the fan or open a window after showers and running water.

Reduce as much moisture as possible.

Clean more often.

Periodically spray the area with a mold prevention or bleach solution.

 You might also enjoy this from Dave 

Should we replace the water supply hose going to toilet?

Dear Dave,
There was a nick in the flexible water line with white sleeve inside. We have repaired it with a connector and two clamps. No leaks. However, there is now a small amount of water visible between the inner liner and hose. Will this eventually become a problem? Do we need to replace entire water supply line? Thanks. —Ron, 2018 28 ft. Minnie Plus 5th wheel

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.



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C. Miller (@guest_240559)
5 months ago

Our solution was to just buy a new toilet!

DW/ND (@guest_240523)
5 months ago

I agree with Bob below. Also bleach is hard on rubber seals altho I use it too. My toilet seal does a similar thing, as indicated in this article, in the spring after winter storage and first two or three fills with standing water over the seal. I just flush it off and it will finally swell up and seal again. The seal has a grainy or rough surface which I think is caused by the bleach – altho the RV antifreeze I add to the bowl for winter storage may also contribute.

Gary W. (@guest_240519)
5 months ago

I’ve heard orange oil spray is better than bleach on black mold.

Dr4Film (@guest_240500)
5 months ago

I use bleach!

Neal Davis (@guest_240499)
5 months ago

Thank you, Dave!

Snayte (@guest_240489)
5 months ago

TSP is banned in many states.

Bob (@guest_240478)
5 months ago

Since the problem is only in the toilet, it does not sound like a water problem. It may be the rubber ball seal deteriorating since the problem returns within hours. It normally takes mold 24-48 hours to grow.

Roger B (@guest_240520)
5 months ago
Reply to  Bob

I took the toilet apart and thoroughly cleaned the china bowl and seal parts with a very strong bleach solution. Including the channel from the ester inlet to the ring of small holes under the rim. That seemed to take care of the problem for a few days, but now it is trying to get going again.

Last edited 5 months ago by Roger B

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