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Thread: Another sewer gas mystery

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  1. #1

    Default Another sewer gas mystery

    We have an intermittent sewer gas problem in one of the two bathrooms in our new home. We really only notice it after using either of the toilets during cool weather. At those times the smell is strong, though. The other toilet has no problem. I replaced the wax ring clumsily; then tried again with a rubber valve instead. The third time I used 2 wax rings Ė one on the floor and one on the toilet horn. Still no good. I also shoved a hose pipe down the roof vent and flushed it out.

    The house used to have a septic tank but is now connected to the town sewer. Why would cold weather bring out the problem and why would the other toilet not be affected? Could the toilet itself be defective? It is one of those all-in-one units. There is enough water in it. The smell is definitely coming from the toilet and my wife swears it is coming out of the water though Iíve never seen gas bubbling up.

    I would be very grateful for any suggestions.

  2. #2
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
    Join Date
    Nov 2005
    Central Florida


    Try covering the bowl of the offending toilet tightly with Saran Wrap or similar. Flush the other toilet and watch and smell what happens.

    Since you're now experienced at setting toilets, you could swap the two toilets and see if the problem moves.

    How cool/cold does the weather have to get? Might it be related to the furnace coming on?

  3. #3


    Hi Mikey,

    Thanks so much for your answer. I will give the saran wrap a try. I did consider switching the toilets but the problem one is a big beast and hard to deal with on my own. Thatís why I wanted to know if the defective toiled theory was in the realm of possibility before I tried that. Itís also possible that my third attempt at replacing the seal was also botched but Iím still in denial about that one. Actually, I messed up one of the 2 wax seals I used and had to remold it into shape. Donít know if thatís a problem and I don't want to face a 4th attempt.

    There was no sewer gas smell for a few days after that until the night temperature dropped to mid 40ís outside. As far as I can remember the furnace never came on but thatís another great suggestion to check out.

    Thanks again.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Wax seals have been around for a long time are cheap and work well. That being said, when I replaced my toilets, I used Fluidmaster waxless seals. Figured, no cleaningoff old wax and no ruining the seal if the toilet is not let down square. Seem to work well.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5


    My 2nd attempt was with the Fluidmaster waxless but that didn't stop the smell either. Hard to know if I botched the fitting somehow or if the seal is not the problem at all.

    Life is full of mystery, isn't it

  6. #6
    Plumber Cass's Avatar
    Join Date
    Nov 2005


    Are you on a well or city water?

  7. #7
    DIY Senior Member molo's Avatar
    Join Date
    Sep 2006
    cold new york

    Default Heavy cold air

    This sounds like a project for an Atmospheric Scientist or Meteorologist. Cold air is heavier than warm air. Air pressure is at the core of venting. That's why in hilly or mountainous regions the valleys frost before the hills. That's why motorcyclists like the hilltops when they're riding at night (even in summer). My high-school earth science teacher use to complain about baseball commentators that claimed the ball would fly farther because it was cold out, because the cold air is actually heavier than the warm air.
    That might begin to explain the temperature mystery. As far as the actuall vent design, I'll leave that to the venting experts. One question I do have;
    Is the trap cracked or have a cleanout at the botom of it that might be leaking?
    I'm curious about your findings, please report back



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