Sewer smell in bathroom

Grey waste tank can smell just as bad if not worst then a black waste tank.

Some RV mfg. have plumbed bathroom sink drain to black tank with an 'air admittance valve' on sink drain line

Non closing AAV can allow stink back inside RV be it Grey or Black






Black tank flush anti-siphon vacuum breaker devices (also installed in bathroom sink cabinet) are open to atmosphere on the black tank side.
Proper working tank vent will pull air IN thru opening....blocked vent will allow odors to come back from tank

check the anti backflow valve for the black tank flush if it has that feature. if the valve doesn't close, it is just like the air admitance valve on the grey tank.

Thanks for all the suggestions. I have tried pretty much all the above except checking the valve under the sink,I will do that tomorrow. I tried cleaning with clothes detergent,the wife has wiped everything down in the bathroom multiple times. I have been fighting this since we got it. I am thinking of pulling the toilet,like suggested.its a domestic. Again thanks

Old-Biscuit wrote:
Check inside bathroom sink cabinet for 'Air Admittance Valve'
Will be on stub pipe just downstream of 'P' trap. Allows air into drain line when dumping waste tank so 'P' traps do not get sucked dry.
Don't close...STINK comes back

Available hardware stores

Yes, it's good to check this valve, but remember, the black tank is vented on the roof! If you are smelling sewer (poo and urine), it's coming from the black tank, not the grey tank. Grey tank is vented with the Air Admittance Valve under the sink, but not the black tank.

I had a similar problem that went on for about 2 weeks just a very short while ago.

First, I dumped the black tank, clean it out by adding water and laundry soap and bleach and driving around to slosh it good and clean. Dumped, and rinsed. That took care of the initial bad smells every time we pushed the toilet peddle.

Now, the trailer started smelling like chlorine, and then I figured it out. The air vent for the black tank IS near the roof air vent over the bathroom. We never use our fan, it's just too noisy. When the air blows in the (wrong) direction, the odors emitting from the black tank vent on the roof was blowing right into the roof vent in the bathroom.... that was the smell. Bad design of the camper (maybe). But at least I figured it out nothing was wrong with any vents or valves, or anything. It's just the way the wind blew.

Now, I'm a little more diligent in keeping the black tank a little cleaner. Problem solved. Chlorine is much nicer to smell than poo any day!

Yours may be just that simple too.

Another thing ... it really pays to bleach around your toilet, the walls and the floors and the outside of the bowl itself. One drop of urine left uncleaned can smell horrid after a few days. And it only takes one drop!

Parrothead Mike wrote:
How about checking the vent cap on the roof? If you remove the cap on the roof you may find that bees or something is blocking the vent with a nest.

Or that the pipe coming up through it isn't too tall and is sealing against the underside of the cap.

The air admittance valve is a good place to start as mentioned above. You might also try pouring water down all drains such as sink and shower to make sure any and all p-traps have water in them to prevent odor.

I have a Dometic 300 toilet. We got a persistent sewer smell and I could not figure out where it was coming from. In desperation, I removed the toilet from the trailer, and voila, no more smell in the trailer. I disassembled the toilet and found that it has an inner and an outer shell, with an "O" ring between them. In my case, the "O" ring, which has a square cross-section, was rolled over so that it didn't seal. I found about half a cupful of black water in between the two shells.

I would recommend you do all the things others have suggested first. Then, if the smell persists and you have a similar toilet to mine, you just might remove it and investigate whether there is black water trapped somewhere.

I'm so thankful my poop dosen't stink. I never have this problem

If you have the toilet fresh water flush,,, run a hose to it and turn it on for about 20 minutes with the black tank valve open so the water and debris can run into the sewer hose. That will take care of the smell. Do not forget to put tank treatment in the toilet and add a few gallons of water after each dump.

Are you using the chemicals like you should be?

In 20years and three RV's we have never had a smell.
I credit it with using the chemicals and the proper amount

Jack l