About five years ago we moved our washer and dryer from a downstairs laundry room to an upstairs location as part of a major remodel. The downstairs water bibs and drain pipe were left intact, but have not been used since the washer and dryer were moved. A few weeks ago we noticed a foul, mildew and rotten egg smell coming from the downstairs drain pipe. It went away the same day, but returned today, (again getting better after a few hours). I thought perhaps the smell happened because water in the "P" trap evaporated, but the water would have evaporated long ago, (nothing has drained into the pipe for the last five years). Any ideas where the smell is coming from, why it took nearly five years to happen, and why it occurs only occasionally? Any help would be appreciated.

Add water and a little vegetable oil to the trap. The smell can come and go depending on air pressure changes.

I wonder if it could stink on and off and you just didn't catch it. And now you are looking for it.

I was just helping my buddy tile his basement bath floor so we had the toilet pulled out. It didn't stink the first couple days when we were working on the room (we plugged it when not working).

I even remarked , hey the toilet pipe doesn't smell bad.

Then his wife did laundry while we were in the room with the pipe unplugged. Peeeee-yew! I think the hot water getting pumped in the pipe enhanced the bouquet.

I'm not a pro. Maybe the pros have a different idea.

wind direction and wind speed factor in sometimes..

Also people tend to walk into plumbing "work in progress" areas to let gas out so no one would suspect it.

Good info, thank you for your reply. Is it bad for the system to simply cap the unused drain pipe?



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