I am finishing my basement. Shower is done, toilet is done, just installed vanity, sink, faucet, and drain. But the sink drains really slow when there is a small amount of water in the sink. But if I fill up the sink fairly full, then open the stopper, the water drains very quickly.
Two potential problems I see: (1) sink is vented four feet from drain (I believe code is 3'), (2) tailpiece is 1.25" and trap is 1.5". Anyone have any experience with this?