The past few days I have noticed a distinct sewer odor in our main bathroom. It is worse when I open the cabinets under the sink. No signs of leakage. OK no problem, I thought. I pulled the P trap, clean as a whistle. Pulled the PVC stub, relatively clean and no signs of obvious blockage. Pulled the stopper plug in the sink. No hair on it at all.

Finally I poured some Draino into the sink and flushed with hot water. When I woke up, the smell seemed to be gone or at least not noticeable. After showering and using the sink, however, it returned!

All toilets have the proper level, and all drains are used daily, so I don't think the traps have evaporated. I have not heard gurgling noises either. Any ideas on what this could be? Thanks for your help!

Climb up on the roof and check the vent pipe for a birds nest or some other type of blockage.

It doesn't sound to me like a clogged vent. If you're sure there's no hair hidden away down there tonight pour 1/2 gallon of bleach and let it set overnight. Next morning boil two large pans of water and flush the bleach out with this. The bleach will began to dissolve any hidden gunk and the boiling water will melt that stinky grease and flush the mess away. Smell better now? Tom

It doesn't sound to me like a clogged vent. If you're sure there's no hair hidden away down there tonight pour 1/2 gallon of bleach and let it set overnight. Next morning boil two large pans of water and flush the bleach out with this. The bleach will began to dissolve any hidden gunk and the boiling water will melt that stinky grease and flush the mess away. Smell better now? Tom

I will give that a try. If it doesn't work, I guess I am going on the roof. Thanks to both for your suggestions.

I will give that a try. If it doesn't work, I guess I am going on the roof. Thanks to both for your suggestions.

OK I did as you suggested. 1/2 gallon of bleach in all drains. Boiling water to flush. The smell has not gone away. I am now thinking it could be a dead animal, but that begs the question, why is the smell aggravated after using water? Also, doesn't the vent stack get larger as it goes down? Wouldn't an animal have dropped through?

I'm still thinking this could be a vent, sorry Tom. If your vent is clogged the traps can siphon dry and allow sewer gas into the room. Try adding just about 3 cups of water to the sink and tub and check in the morning. If the smell is gone I'm going with vent but it would have been nice to hear the tell tale gurgling. Even a dead squirrel in your vent would not be smelled in the house unless the traps siphon, and yes vents can be larger near the basement but frequently start and stay 4" all the way to the roof.