Sewer gas has been leaking into our main floor bathroom for the past couple of months. After several visits from our plumber with no success fixing the problem, he's told us he's stumped and doesn't know what else to do.

Here's what we've tried so far:

  • regularly run water down all the drains in the house, & made sure the p traps in the affected bathroom aren't dry or leaking

  • poured boiling water, baking soda & vinegar down the drain multiple times to deal with any biofilm

  • replaced the toilet wax seal and caulked around the toilet base

  • checked the soil stack is venting properly at the roof, and ran water down it to ID any leaks up the line from the bathroom - none we could see where the pipe is visible in the attic or from a cutaway in the bathroom wall

  • flushed the basement/foundation drain

  • vent missing on the plumbing under the sink, so we had one installed

After doing all this, the sewer gas smell has improved some, but is definitely still coming into the main floor bathroom, especially when we run the bathroom exhaust fan when the door or window is closed, or when the weather is warm.

Any suggestions for what we should try next? Smoke test/camera diagnostic to look for a leak somewhere down the line from the bathroom?

  • I suspect you're about to land on bigger labor dollars, because the next step is likely going to need to be a real air leak test, which is a bit of a headache once the fixtures are all in place. Someone with more plumbing experience than me will hopefully have a full answer.
    – KMJ
    Oct 23, 2023 at 19:50
  • Try this before you spend any more money: diy.stackexchange.com/a/281057/79373
    – MTA
    Oct 23, 2023 at 20:05
  • Is it coming from a floor drain? Maybe from the main vent but air is coming out the top and back into the structure?
    – rogerdpack
    Nov 23, 2023 at 0:09

1 Answer 1


Make sure it's not a natural gas/propane leak. They can smell the same.

If you know how to relight pilot lights, turn off the home's gas supply and see if it dissipates.

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