I'm trying to remove a shower stall in my basement to correct a leak in the incoming water supply pipe. In order to get in the back, where the supply lines are, I must move the shower stall out of the way. It seems that the drain is the only thing preventing me access to the pipes. How do I remove the plastic drain cap and gasket without destroying the PVC pipe drain? Does the drain cap unscrew or do I need to pry it off and chance damaging the pipe and gasket. Any help would be greatly appreciated!!