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?