It could also be some gunk in the overflow tube of the lav basin.
Try cleaning that first.
I appear to be the victim of a previous owner's remodel.
The right sink on a double vanity isn't vented correctly, I think. When I get my nose down in there it stinks, only when the water is running/has just run. The left sink, no problem.
I'm fearful of what I'll find if I go through the wall; on the plus side, there's lots of room.
I've been reading here what *should* be back there...Am I missing something obvious? Or is it just a case of tearing out sheetrock to see what's what?
Thanks, I tried that. It seemed odd only one sink would burp gas?
You tried WHAT? Why should it be strange for just one sink to do it if it is the overflow which your description indicates it is? If only one has a buildup, then only that one will give an odor.
HOW did you clean it? Unless you used a strong chemical to "burn" the debris out, it is still there. If the odor happens when you turn the faucet on, then it IS coming from the overflow.
Just posting to say you boys were absolutely right, I went more serious on the chemicals to clean the overflow again, and the smell has gone for good this time.