Washing machine drain lines are often simply draped over the edge of a utility sink, where they empty into the sink's drain. But this practice is not approved by some building codes, and the machine instead drains directly into a drain line. This type of drainage can be accomplished by adding a new standpipe drain to an existing wall-mounted sink drain line.
Things You'll Need
Y-fitting PVC waste pipe sized for the existing drain line
90-degree PVC elbow
2-inch diameter PVC standpipe drain (at least 36 inches long) with trap assembly
PVC solvent glue
2-by-4 wood backer board (if needed)
Measure the PVC Y-fitting to determine what length of pipe you need to remove from the existing drain line in order to insert the fitting. Mark this distance on the drain line, then make two cuts with the reciprocating saw to remove the old section. Make the cuts as straight as possible, perpendicular to the length of the pipe.
Remove any burrs or rough edges from the cut ends of the drain pipe with the utility knife. Coat the inner surfaces of the two parallel ends of the Y-fitting with PVC solvent glue. Insert the cut ends of the drain pipe into the ends of the Y-fitting, and push the fitting in place. Make sure the Y-fitting is oriented so that its third, angled opening is at the same level as the drain pipe, not above or below it. Let the PVC solvent glue dry completely.
Coat the inside surface of the 90-degree PVC elbow with solvent glue, then push it onto the remaining opening on the Y-fitting, orienting the open end of the elbow downward towards the floor. Let the solvent glue dry completely.
Coat the inside surfaces of the ends of the P-trap with solvent glue, then press one end onto the open end of the 90-degree elbow, and the other end to the PVC standpipe. The standpipe should be pointing upward, running parallel to the wall, and as close to the wall surface as possible.
If the installed standpipe is too tall, use the reciprocating saw to cut it down to the appropriate height. The top of the pipe should be taller than the highest water level in the washing machine, at least 34 inches above the floor.
Wrap the pipe strap around the top of the standpipe, and fasten the strap to the wall using 1/2-inch screws. If the room is unfinished, attach a 2-by-4 wood backing board across the exposed studs, then fasten the pipe strap to the backing board.
Hook the washing machine's rubber drain hose into the open top of the standpipe.
You may want to dry-fit the Y-fitting, elbow, trap and standpipe before gluing them, to make sure they fit together correctly. Once the solvent glue dries, the connections cannot be loosened, moved or adjusted.
Check your local plumbing codes before beginning work, and obtain any required permits.