How to Install a Utility Sink Drain

Installing a utility sink drain can be less difficult than installing a drain in a kitchen or bathroom sink because you have access underneath it. Because the sink is movable, though, there probably isn't a drain stub-out exactly where you want it, and you may have to make one. It's a good idea to locate the sink near a waste line to minimize the length of pipe you need to connect it. Don't forget to vent the sink drain. It's a requirement of the plumbing code and will keep water flowing.

A P-trap is an important component of a utility sink drain.
  1. Cut into the existing waste line at the closest approach to the sink with a hacksaw. Remove a section large enough to accommodate a wye fitting with a 2-inch outlet. A wye is a drainage fitting shaped like a "T", but with a sweep inlet instead of a straight one. Glue in a plastic wye with PVC cement if the drain is PVC, being sure the inlet is facing the sink and has a slight upward tilt. If the drain is cast iron, attach a rubber wye to the pipes by tightening the metal straps on either end with a screwdriver.

  2. Attach a small length of 2-inch PVC pipe to the wye outlet, either by gluing it in or tightening the metal strap on the wye with a screwdriver. Glue another wye to the pipe with the inlet facing up and toward the nearest vent attached to the existing drain line. Cut into the existing vent at a convenient location and install another wye with the inlet facing the first wye. Connect the two wyes with 2-inch PVC pipe, gluing the ends of the pipe to the wyes.

  3. Glue a small length of 2-inch pipe to the other outlet of the wye, then glue on a 2-by-1 1/2-inch P-trap adapter. It has a compression fitting on the end so you can connect the 1 1/2-inch drain pipe from the sink.

  4. Apply plumber's putty liberally to the underside of the strainer of a drain assembly and set the drain into the hole in the bottom of the sink. Screw the retaining nut on from underneath and tighten it with slip-lock pliers. The drain should have a length of 1 1/2-inch pipe extending down from it, called the tail piece.

  5. Set the sink in position. Remove the nut and flange from a P-trap assembly and slide them up along the tailpiece. The nut should go first, with the threads facing downward, followed by the flange with the tapered end facing down. Slide the mouth of the trap up along the tailpiece so that the outlet of the assembly is high enough to provide a downward slope in the pipe that extends from the other end of the trap to the drain. Insert the flange in the opening and screw on the nut, tightening it by hand.

  6. Assemble a length of 1 1/2-inch pipe that extends from the outlet of the P-trap to the drain, gluing in appropriate fittings as needed. Insert one end in the compression fitting on the end of the P-trap and the other in the adapter attached to the wye in the drain. Tighten both compression nuts by hand. Support the pipe, if needed, with plumbing straps.

About the Author

Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since 1975. As a landscape builder, he helped establish two gardening companies.