My bathroom sink has always drained very slowly. Recently the room was renovated and the water continues to drain poorly even though the hardware is all new up to the wall. While trouble shooting, I found when just tail piece coming down from the sink, the water drains at an acceptable rate. As soon as I attach the P-trap, the water virtually stops draining even if the end of the P-trap is open to the air rather than draining in to the wall's pipe. The P-trap is new and I have inspected it that there is no blockage. I would appreciate some advice on further steps to take as what I'm observing doesn't even seem to match how water actually works.