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?