Quote: Originally Posted by bcreilly We moved into an old house (1940s) in the summer of 2013. Since moving in, we have noticed a fairly random but persistent sewer smell in the basement. The only patterns that we have noticed are: a)The smell seems to be worse in the colder months. b)The smell seems to occur most often when we do the laundry. My initial thought was that there was a problem with the drain line. We had plumbers come in in March of this year and replace the clay drain line with ABS. Unfortunately, that didn’t seem to fix the problem. In the basement we have: a)Washing machine dumping into a laundry sink. b)A bathroom with a sink and toilet c)A floor drain (the ac/furnace drains into here) Can anyone suggest ways to troubleshoot where the smell is coming from? My current thought is that the laundry sink is not vented properly so when we run the washer the water in the laundry sink trap is getting siphoned out. Is there any way to check this? Pictures attached show how the laundry sink drains and is vented. In the picture you can see the laundry sink (left pipe) and washroom sink (right pipe) connecting to a single drain line. Both sinks have p-traps. The top pipe I assume is the vent, but to be honest I lose it once it goes into the wall. That said, the main stack is about five feet to the left of this picture and a) I can't see how this pipe would make its way back to the stack b) there are no other holes in the roof. I should also note that there isn't any other real evidence of an issue with venting... the sinks seem to drain OK and I haven't noticed any bubbling in the toilet etc. Thanks, Brian The laundry sink is S trapped, probably not a problem when you run the faucet on the laundry sink, but very likely to siphon the trap with the high volume discharge of the washing machine.

Thanks for your comments both. Frodo: That was one thing I considered (definitely makes sense given what time of year the smell generally occurs). That said, I have checked the floor drain and it seems to be at a good level. I will continue to monitor that though and add water periodically. phishfood: Please see the attached photo which shows the trap for the laundry sink. Isn't that a P trap?

when was the last time your ac ran? that p trap for the floor drain, with the ac draininging into it. pour a 1/2 galon or water in there during the winter mths. your heater does not make condensate. bet that trap is dry