Presently I have a tub drain that has corroded to the point of losing the spindles at the bottom…the tub/shower unit is a prefab fiberglass unit…the pipe that the drain is threaded into is pvc…obviously I have nothing to grab onto to unscrew the drain…I have tried with pliers and with pressure of expanding the jaws to unscrew with no success…is there any substance like wd-40 that can loosen the pipe joint compound and putty?…how would you attack the problem and what tools would you use?…please respond asap…thanks…paul