Dom, thanks for the reference between AAV and mechanical. I did know the difference, should have used one of those smilie things. Jerry indicated by his post that the problem may be related to it not being a AAV. My thought was that they both have the same function in life just different designs. The reason for the vent in the first place, is to prevent siphoning and keep the water in the trap. I have yet to see a vent problem prevent water from running down the pipe... I think one would do better taking a quick inventory of valuables that little Johnnie might have sent down the swirley!