I have a 7-year-old house. The bathroom has double sinks. On only one of the two sinks, I get a sewer smell briefly after I turn on the water. It is the same for both hot & cold water, and the sink right next to it does not ever have the same smell. It dissipates within 10 seconds or so after the water starts running.

I've pulled the trap completely apart and there was no sediment or clogging in it at all. I've also replaced the faucet & drain recently (for cosmetic reasons) and the problem persisted, so it's not because of a clog, hair, etc. In the drain.

I'm assuming this has something to do with improper venting of the drains in that area, but I 1) can't see the plumbing without destroying my bathroom walls 2) don't know enough about drain venting to know a problem if I saw one.

Is there any more troubleshooting I can do without tearing into the walls to determine the cause of the problem? Are there any alternative fixes such as a back flow preventer on the drain that might fix the problem without having to really know the cause?

Thanks in advance for any advice!

Mike

A few questions. Is there just one trap for both lavatories or are there two traps? Are you quite sure the smell's coming from the drain and not the water? Have you removed the aerator and checked? Is there any sound from the trap as the lavatory drains?
Did this problem just start or has it been ongoing? Back to you, Tom

There are 2 separate traps for the sinks. I'm not 100% sure that the smell is coming from the drain, but it's definitely NOT coming from the water. I can fill a glass and take it away from the sink and there is no smell at all.

The problem has existed since I bought the house over a year ago and changing out the entire fixture (including the aerator, stopper, drain, etc.) caused no change to the smell.

I have noticed that in all 4 of my upstairs sinks (in 2 different bathrooms) the drains "burp" as they drain when I turn the faucet on full blast. None of the other 3 sinks have the smell though, including the one right next to the offending sink.

Mike

I have noticed that in all 4 of my upstairs sinks (in 2 different bathrooms) the drains "burp" as they drain when I turn the faucet on full blast. And with that one sentence you just made my job much easier.
Here's what I think is happening. A "burp" indicates a blowback of sewer gas. This is caused by a partial blockage in the drain line. You open the faucet full blast and drain the sink. The discharge goes down the drain line, hits the partial clog and bounces back sending a bubble of sewer gas ahead of it. (Your burp.) before draining away.
The solution would be to snake the drain line from that sink. How's that sound to you? Good luck, Tom

Thanks for the advice speedball1! I'll get a snake and give that a try. I'll post back with the outcome, although it may take a couple of weeks until I get to it.

Mike

I wouldn't let it slide too long. Sewer gas is harmful to your families health and then methane content makes it explosive. Regards and let us know how you made out. b Tom

Snaking the drain didn't make any difference, so I dumped a bunch of bleach down the drain, let it sit for an hour or so, then flushed it with a large pot of boiling water as recommended on another thread on this site. That was in early October and the smell has never returned! Thanks to everyone for the advice. This site has been a huge help!

And we thank you for the update, If you can use us in the future we're as close as a click. Cheers, Tom