If, when renovating a house, the bathtub is moved to another location, the bathtub drain, or sewer pipe, will also have to be moved. This sewer pipe is connected at one end to the bathtub's P-trap, and the other end to the connecting coupling that is attached to the house's main sewer line. The sewer pipe itself is made of either ABS (Acrylonitrile Butadiene Styrene) black plastic or white PVC plastic. Both types of sewer pipe are glued into position.
Mark the sewer pipe 1/2 inch above the existing P-trap, near the bottom of the bathtub's drain/waste pipe assembly. Make a straight cut through the pipe at the mark using a hacksaw. Remove any burrs with a Tradesman's knife.
Place the bathtub in the new location, and mark a circle on the floor at the location where the bathtub's drainpipe will enter down through the floor--this hole will be slightly larger than the diameter of the pipe. Cut out the hole by drilling around the perimeter of the hole--use a 1/2-inch wood bit. Rest the bathtub in position so that the cut end of the drain/waste pipe assembly enters down into the hole.
Cut the bathtub sewer pipe 3 inches along from the point where it attaches to the connecting coupling's side spout (the connecting coupling is attached to the main sewer line). Make the cut straight, and remove the burrs. Now remove the old sewer pipe.
Apply ABS glue around the cut pipe, as well as one inside end of an ABS coupling (this coupling may be angled or straight, depending upon the new location of the bathtub). Push the coupling onto the end of the pipe and hold for 30 seconds.
Glue one end of a new piece of sewer pipe, and the other inside end of the coupling. Push the pipe into the coupling, holding it for 30 seconds. Now measure, cut and glue together new pipe and couplings until you reach over to below the bathtub's drain/waste-pipe assembly.
Assemble a new P-trap, which usually comes in three parts, but don't glue it together. Push the vertical end of the P-trap up onto the cut end of the drain/waste pipe assembly, and the other end onto the end of the sewer line. If it fits so that the vertical part of the P-trap is directly vertical, take the P-trap off and glue all parts into place. But if the P-trap is not vertical, cut the appropriate amount off the end of the sewer pipe to make the P-trap vertical when installed into place.