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Ask Dave: Why does my RV smell like sewage after I dump the black tank?

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. Today he discusses the possible causes for why the RV smells like sewage after dumping the black tank.

RV smells like sewage after dumping tank

Dear Dave,
We have a 2014 Winnebago Tour. My issue is that when we’re leaving a campsite and dump the black tank, for the first 30 minutes we get a stink from the toilet. I have looked and looked for any possible breaks in the vent pipe and just can’t find anything. We have tried leaving windows open, and tried running the fan (I know that’s a no-no). We have left water in the bowl (and it stays in the bowl for hours). I am out of ideas. Any suggestions? —Jim

Dear Jim,
I don’t know that running the fan is a no-no. However, I think it would make things worse as it would be drawing air from the black water tank.

If you have a good seal at the toilet valve that holds water, I would check the toilet base to make sure it is sealed properly there as well. There should be a rubber gasket around the hole in the floor that seals. If it’s cracked or misaligned, it would allow odor from the black water tank to come inside. You might need to take the toilet out to inspect. Before doing that, check to see/smell if the odor is more intense at the base.

Clean the black tank thoroughly

One other item I would suggest is cleaning your black water tank out thoroughly. If you are getting sewage smells after dumping, it indicates the black water tank still has sewage in it and might not have the proper chemical. I would suggest using Tank Blaster by Thetford for a thorough cleaning, as recommended. Then, when dumping, you should dump and fill at least twice.

Since it’s a Winnebago Tour, I assume it has a black water flush valve. If so, hook up a water hose and fill the tank after the initial dump. This will spray water around the sides and help clean everything off. Then dump again. You will be amazed at how dirty the water is the second time. Sometimes it even takes a third time. It’s a good idea to use a see-through or opaque adapter at the end.

If you inspected all your vent lines, the last thing I would suggest is changing out the vent covers with a Cyclone model that pivots with the wind and actually draws air out while you are driving.

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Malinda Rhodes
22 days ago

Something else to try – make sure there’s water in the toilet bowl before emptying tank. It can help keep the odor escaping up through the toilet. If the bowl doesn’t hold water, check the valve seal to see if water in bowl is seeping out and, if so, replace the seal.

Cecilia
22 days ago

Something to consider…are you sure the smell is from the black tank? Check out the RVGeeks recent video called Mystery RV Gray Water Stench.

Irv
22 days ago

re: “Then, when dumping, you should dump and fill at least twice.”

Please don’t do this if there’s a line behind you at a dump station! I got stuck behind someone doing this for 45 minutes. I have no idea how long they were there before I got there.

If it takes more than 15 minutes and you’re not done, pull around and get back in line behind them.

A dump should only take 5 or 10 minutes. If there’s a line in front of you, get your hoses ready while waiting on the RV in front of you. If there’s someone behind you and room to pull forward, do so before putting your hoses away.

Only rinse out your tanks if you’re headed home to storage. The 15 minute rule should apply.

Marty P
22 days ago

Maybe simpler than that. In our MH the bathroom sink drains into the black tank. If the sink p trap dries out it lets fumes into the bathroom. Adding some water to the sink usually solves the problem.

Ron Lane
22 days ago

It seems everyone has their own idea of how and/or what to use in their black tanks. Here is mine. First, I never use any black tank chemical..never. What I do is starting with an empty tank, I use plain ol liquid laundry detergent (1 cup) along with about 3 – 5 gallons of clean water. Sometimes I’ll put a cap (or two) full of Calgon water softener in with it and then drive to my next destination. The agitation caused by the motorhome rocking/vibrating during travel will “wash” the inside of the tank. Once at my destination, I’ll add another 10 gallons or so and then drain the tank. Once drained, I’ll add about five gallons of clean and use the tank normally.
Depending how often we travel, I will do this about every 5th tank full. This keeps the tank operating as designed, sensors operating perfectly and as an added bonus, never allows odors.
I have been using this procedure for my past four rv’s (everything from a small travel trailer to our current 44′ motorhome).

Wayne Caldwell
22 days ago

Dave, your response reminded me of our ‘smelly situation’ earlier this year. Our toilet flush valve broke and, being one of those DIY kinda.guys, I ordered a replacement, removed the toilet and replaced the valve. Proud of my accomplishment, I reinstalled the toilet on top of the rubber seal and tested.the flush valve. Everything worked like it should. However, on our next camping trip, we noticed the ugly smell and moisture on the floor. When we returned home I re-removed the toilet and found I had a kink in the sponge rubber seal and that was causing the problem. I ordered a replacement and this time installed it onto the toilet’s down pipe, reinstalled the toilet and had no more stinky odor.