HELP! My new shower in the basement is exactly the same as the old one except for one thing. The drain assembly needs to hook up to a 2 inch inside, 2 and 3 eigths outside diameter pipe (black PVC 2") The drain pipe in the floor (concrete) is 1 and 3 Quarters inside and only 2 and an eigth outside! The shower comes with a special seal that fits over the pipe and thus it needs to be the right size. So....is it possible to get a slightly different sized seal? Or how do I go from this old metal pipe to the newer PVC type of the right size?