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 Control, available on Amazon here.
It is EPA-registered, bleach-free, odorless, and VOC-free.
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.
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It could also be that the black toilet seal is failing and coming apart. The fact that the black substance is only below the water line points toward this. How old is the seal and does it still hold water reliably?
Thank you for sharing this information, Dave! Sounds like a lot of work in the extreme to avoid many potentially health-damaging situations. Good to understand how pervasive mold can become. Have a great day and safe travels!