How to Connect a Plastic Pipe to a Metal Pipe in a Wall Sink Drain

Plastic drain assemblies connect to metal drainpipes with flexible adapter fittings.

Although it appears impossible to connect plastic and metal pipes, a simple adapter fitting bridges the gap between dissimilar materials and pipe diameters. The easiest adapter to use for an under-sink drain assembly to wall drain connections is a flexible, rubber sleeve called a "no-hub coupling." The coupling slips over the ends of both cast iron and plastic pipes and attaches to the pipes with screw-tightened band clamps. The adapter's band clamps tightly seal the joint between pipes without glue or extensive tightening by wrench.

Things You'll Need

• Tape measure or calipers
• Flexible coupling
• Emery cloth
• Rag
• Nut drivers or screwdrivers

Instructions

1. Stretch a tape measure or calipers between opposite sides of the pipes' outside surfaces to determine the pipes' diameters. Alternatively, inspect the pipes' outer walls to find markings that indicate the pipes' diameters. Note that actual pipe diameters differ from the nominal dimensions, which manufacturers use to describe fitting size. Select a flexible coupling equal in diameter to the metal pipe on one side and equal to the plastic pipe on the other side.

2. Rub the pipes' open ends with emery cloth to remove burrs, grease and dirt. Clean the pipes' ends with a rag. Insert a nut driver over the coupling's band clamp screws or insert a screwdriver into the clamp screws' slots. Twist the screws counterclockwise to loosen the band clamp. Leave the clamps dangling around the coupling's ends.

3. Slip the end of the coupling that corresponds in diameter to the metal pipe over the metal pipe's end. Twist and push the coupling to position the clamp over the pipe's outer wall. Twist the clamp's screw with a nut driver or screwdriver to tighten the clamp around the metal pipe's circumference. Tighten the nut roughly one-quarter turn past hand tight.

4. Slip the plastic pipe into the remaining open end of the flexible coupling. Shimmy and push the plastic pipe until the pipe fully enters the coupling and the coupling's clamp rests above the circumference of the plastic pipe's outer wall. Twist the clamp's screw with a nut driver or screwdriver to tighten the clamp around the plastic pipe's outer wall. Tighten the nut one-quarter turn beyond hand tight.

5. Turn on the fixture that drains into the new connection. Run water through the new connection and check both sides of the coupling for leaks. If you find a leak, slightly tighten the coupling's band clamps.

Tips & Warnings

• If the plastic pipes are too long to fit within the coupling, cut the pipes to size with a hacksaw.

• If the plastic pipes are too short to fit into the coupling, add a slip-joint coupling and extension pipe to the end of the existing drain assembly.

References

• Texas A&M University: Get to Know Your Plumbing Pipes and Tools!
• Ace Hardware: Working With Plastic Pipe