How to Replace Cast Toilet Drain Pipes

Find the intersection of the cast drain pipes and the bottom of the toilet underneath your floor. Remove the drain pipe from the end of the toilet flange elbow joint with a grinder and metal cutting disc. To support the pipe, install a pipe-hanging bracket about a foot away from your cut.

Cut the other end of the pipe at the intersection to your home's main drain stack the same way, after installing another support bracket near the end of the pipe. Once both ends are cut, remove the pipe with an assistant’s help.

Install a PVC-to-iron pipe fitting on the end of the toilet flange elbow joint and at the intersection of the drain stack. Tighten the metal collar with a screwdriver to secure the connection.

Install new PVC drain pipe between the two fittings. Measure the distance between the fittings, cut the drain pipe to size with a hacksaw and slide both ends of the pipe into the fittings without cement. Adjust the pipe size, if needed, then coat the edges with PVC cement and install back in the fittings. Let the cement dry for up to eight hours or per the cement label instructions.