Unusual plumbing question

[McClain]

It sounds like the issue might be a venting problem or something related to air pressure changes in the pipes. I had a similar situation and found that a faulty or improperly placed air admittance valve was the culprit. If the smell is coming and going, it could be due to shifting pressure in the system. A plumbing service company could check it out and figure out exactly what’s going on.

 

[KassadiXX]

If you’re dealing with air in the lines after shutting off the main valve, try opening multiple faucets to let the trapped air escape. Sometimes, flushing a toilet helps clear it faster.