I need to replace an old drain pipe (late 1940s, early 1950s) which goes into a stub coming up through the tiled floor. The flange that screws down onto the trap has corroded and crumbled into small pieces. The drain pipe that fits into the stub pipe in the floor won't budge and I'm afraid to put much torque on it. The former owners of the house did not remove the tile floor but tiled on top of tile. Is it possible there's a set-screw holding the drain pipe in place in the stub pipe, which is now hidden below a layer of floor tile? How were these pipes typically held in place? Is it just a caulk or plumbers putty seal? Any special solvents available to loosen it up, if so?