Smelly Sink/Vent

I have a little sink with very tight clearances and several months after the completed house I noticed a foul smell and traced it to a small sink in a small bathroom. The plumber suggested I put a p trap in the wall in addition to the bottle trap on the sink. I have isolated the smell to this drain. When a plug is placed in the drain without the sink attached the smell stops. While I was placing the p trap in the wall I noticed an open drain pipe that had been drywalled over. I cut the drain line to the sink in question and added the p trap and attached it to the found drain line. I also plugged up the prior stub line that went to the drain. I am attaching photos. I can leave the drain pipe open now and for most of the time there is no smell however there are times when the smell comes. I have installed the sink back on the drain but due to the clearance issues, the tailpiece touches the bottle trap and has a slight angle to the drain in the wall. I have tightened up the 1.25 to 1.5 pvc washer as tight as it can go. I have taken apart and put back the bottle trap several times and everything still seems tight but alas the smell returns. What do I need to do to fix this?

Fixtures are not allowed to be double trapped.

Aren't you curious as to why there are 2 drain(?) lines there?

Is there a vent anywhere?

I don't follow the meaning of, "I can leave the drain pipe open now...".

I think both of those horizontal lines are trap ares off the drain(hopefully) with a vent. A technically approved wet vent. But I would have to see what’s in the wall. It’s pretty obvious that your trap is getting sucked dry somehow and you get sewer gasses back through the sink. Can’t do two traps. You could install an AAV right behind the trap at the sink. That might handle your problem.

RenewDave said:

I think both of those horizontal lines are trap ares off the drain(hopefully) with a vent. A technically approved wet vent. But I would have to see what’s in the wall. It’s pretty obvious that your trap is getting sucked dry somehow and you get sewer gasses back through the sink. Can’t do two traps. You could install an AAV right behind the trap at the sink. That might handle your problem.

Click to expand...

Trap arms.

The reason there was a second trap was there are 3 sinks that are on the vent, 1 shower and 1 toilet. 2 are on one side of the wall and the 1 in question on the other side. The drywaller covered over the drain stub outs and when exploring for the drain, I suspect they only found 1 put the split for the two sinks outside the wall and forgot about the other drain.

The vent is just to the left of the stud shown on the left side of the image probably 8 inches from the trap in the wall.

I meant that when I test the smell now, I can leave the drain open and no smell comes out except occasionally because of the trap installed in the photo.

Yes both of the horizontal lines shown in the original image were trap lines off a vent on the left (not shown) of the image.