I have a kitchen sink, which uses a studor vent underneath it, that had been working since we built a new kitchen in the center of our house. For about 8 years, it drained well. last spring it began to drain slowly and then wouldn't drain at all. I tried to repair myself, including putting in a new studor, but failed to fix it and called an experienced, very well recommended plumber. After about 90 minutes of trying to get it to drain, including fully snaking it, he figured out it would only drain properly if we replaced the studor valve with a fixed, non-venting cap. He said he has never encountered anything like this in his life. If we use the studor vent it drains very slowly. If we remove the vent and put in a fixed cap, with no vent, it drains normally. This doesnt make any sense to me either. Today, the sink started draining very slowly again, with the fixed, ventless cap on. Not sure what to do. Any advice is greatly appreciated. Thank you! JP

i truly makes no sense.
snake it again..

A Studor vent OR a cap, both seal the drain against positive pressure and positive pressure will NOT allow the sink to drain. The stoppage does NOT have to be in the sink drain, it can be anywhere in the system depending on how the piping is installed.