I am DYI installing a 2 piece fiberglass shower stall in my basement had the proffessional plumbers plumb in the drain line all the way to the p trap under my concrete floor. I think I mis-measured the pvc riser coming from the p trap that connects to the compression drain on my shower. Its already glued to the p trap. I think i have two problems. One the riser pvc isn' 100% level not sure if that is really a problem its not off by much, and it seams the stall i have has wiggle room. 2nd the rubber seal inside the drain that compresses after you tighten it down is above the pvc riser not under. Is this going to cause leakage? Can i cut about 1/4 off the rubber seal so that it is below the threaded nut that compresses it down? Any information is much appreciated.