Where to begin!!! Let's start at the top and work down. #1: A washer drain is not supposed to be an air tight, solid connection. That's why the washer drain hose has a crook in the end. It is intended to hook into the open end of the standpipe. #2: The standpipe should be 2", not 1-1/2". New machines require the larger pipe because they drain very quickly. #3: You do not have a P trap. What you have is an illegal S trap. #4: Related to #3, you have no vent. Fixing this mess really isn't going to be too difficult. Take out what you have down to the elbow coming out of the main drain. Turn the elbow so it is parallel to the wall. Put a 2" nipple into the elbow, then a 2" tee into that nipple. Continue with another 2" nipple and a 2" P trap. The vent comes out of the tee. Out of the P trap put another 2" elbow and finally a 2" standpipe. Not sure and a AAV is OK for a washer. Ideally, the vent should connect to an outside vent.