Forum Discussion

chilly81's avatar
chilly81
Explorer
Mar 05, 2017

Bathroom odors coming from toilet-to-floor gasket seal?

I've read a bunch of the existing threads on this common problem and don't think I have a solution yet. 02' trailer. Have always had a little sewer smell after travelling but now it's getting more consistent even on breezy days.

-All traps are full.
-Stacks vents are clear and it's worse on breezy days (makes sense).
-Air checkvalve under sink looks good.
-I'm *pretty* sure it's black tank smell because when I unscrewed the air vent valve under the sink (gray) to check it I almost died, and it seemed to be a different odor. Plus, it really doesn't seem to be emanating from under the sink or from the shower side of the room.
-Toilet flapper seal holds water fine.
-Sniffing the little overflow trap hole in the toilet - doesn't seem to be coming from there - so I think that trap is OK.

So I still can't really pinpoint it except it really seems to be coming from the toilet side of the bathroom and I think it's black tank smell.

I can see the front of the gasket looking under the flush pedals, and it looks OK from the front.

Would it be a waste of time to pull the toilet and check or replace that seal? I'm at a loss.

Any advice? Not looking for waste treatment solutions - just plumbing and mechanical please.
  • bjlakatos1's avatar
    bjlakatos1
    Explorer
    Mar 06, 2017
    A friend had a dometic toilet in his new rig. After about a year, he kept smelling foul odor despite how much he cleaned the toilet and surrounding area. He pulled the toilet to find out there was a seal in between the top and bottom half of the toilet frame that was allowing waste to collect inside the toilet frame. It never leaked due to low volume but it always smelled of urine, etc. He got the next model up (i think a dometic 320) and the design was changed and the leak/odor was gone.
  • doxiemom11's avatar
    doxiemom11
    Explorer II
    Mar 05, 2017
    I would change the air admittance valve under your sink for $20 first before tearing into the sewer system. Grey water smells as bad or worse than the black and you really can't tell that the valve is good by looking at it.

    Also - check your batteries. Have read they will give off a very offensive odor if they are low on water and most confused it with sewer smell.

    We had an issue of odor when traveling. DH found that the vent pipe had slipped down into the tank and wasn't really venting. He got on the roof and pulled it back up where it belonged - fastened in place and no more odor .
  • chilly81's avatar
    chilly81
    Explorer
    Mar 05, 2017
    Well that's good to hear it's not a massive job (like home toilet). I think I'm going to do it just for piece of mind. I'll be on full hookups for a month starting tuesday, so I'll flush everything out and use one of those stink killer additives before I open the mouth of hell.

    @j-d: mine does indeed have that overflow... that's what I was referring to smelling up close. I believe it has a trap inside and it has water in it and I can't detect a smell coming from that hole.

    @garyemunson: I did pull the air valve off and inspect, and as you say - a 02' trailer's gray tank smells like death itself once that valve is off. The smell was not the same as my lingering odor though - so I really think it's the black. The valve really looked to be in fine condition, and the kitchen one is certainly fine. If this doesn't work, I'm sure they are cheap though and I'll try one anyway.
  • RJsfishin's avatar
    RJsfishin
    Explorer
    Mar 05, 2017
    R&R the turlet, check the wax ring, and check that the complete turlet is flat on the floor,....that no carpeting is under it anywhere.
  • dougrainer's avatar
    dougrainer
    Nomad
    Mar 05, 2017
    j-d wrote:
    Some Thetford toilets had what we called a "vent" that they called an "overflow" which was a little hole up by the rim connected down to the outlet, below the flush valve. I think they've discontinued that, but I do know they recommended plugging/sealing them to control "odor."


    Yes, they have a plug kit they will send you if you have the overflow drain hole. IF the lavy sink vent smells the same as your odor, then odds are it is NOT the black tank. But, as I have told in previous posts, DRAIN both tanks and flush. Install a cup of Pine Sol in the toilet tank and test. IF the odor you get in the RV is Pine sol, it is a black tank problem. If NO odor, then your problem is the gray tank. IF you have a Sealand brand toilet (the brand had the overflow holes) the gasket was more pliable foam rubber and they dry out and then leak both water and odors. How old is the RV? Doug
  • j-d's avatar
    j-d
    Explorer II
    Mar 05, 2017
    Some Thetford toilets had what we called a "vent" that they called an "overflow" which was a little hole up by the rim connected down to the outlet, below the flush valve. I think they've discontinued that, but I do know they recommended plugging/sealing them to control "odor."
  • Dave_H_M's avatar
    Dave_H_M
    Explorer II
    Mar 05, 2017
    I had a mystery deal with my toilet. Turned out the flange was not sealed properly/totally to the down pipe. Some silicone took care of that.

    Redoing the flange gasket is a piece of cake (once you get past the smell :R ). As I recall there are different thicknesses, so if your situation permits, it my save some some time and running to yank the toilet first. Course if your supplier has two thicknesses, you could buy the both and later return the one not used.
  • JoeH's avatar
    JoeH
    Explorer III
    Mar 05, 2017
    It takes about 10 minutes and a $4 closet flange gasket to pull the toilet/replace the seal and reinstall the toilet. I had to do mine a few months ago.
  • garyemunson's avatar
    garyemunson
    Explorer II
    Mar 05, 2017
    I'd replace the undersink air valve. If it's never been replaced, it's well beyond it's 'sell by'date! An '02s greywater tank is going to stink just about as bad as the black. Plenty of greasy dishwashing goop stuck to the inside of the tank over the years reeking. The 'worse on windy day' comment really makes me suspect the air valve. After 15 years, the soft rubber seal is bound to be cracked/wrinkled/stiff.
  • Son_of_Norway's avatar
    Son_of_Norway
    Explorer
    Mar 05, 2017
    I would pull the toilet. This happened to me, and it turned out that there was a crack in the pipe between the toilet and the blackwater tank.

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