I have a leak coming from somewhere under my bathtub. I have one of those fiberglass tub/shower combos. I used some Liquid Plumber to try to unclog the drain and I forgot to go back and run hot water through the drain. The next morning I had water leaking from under the tub in the bathroom floor. What is my most probable cause for the leak? Also I have removed the drain in an effort to access the rubber seal, but the seal is under the tub, not the drain, so what would be my next step?