How to Replace Drum Traps With P-Traps

Steve Sloane

Drum traps sometimes are found in older houses beneath bathtubs in the sewer lines. Their purpose, similar to P-traps, is to stop sewer gases from entering through the sewer line and back into the bathroom. Newer P-traps work in a way that when the bathtub water is drained, newer sewer water moves into the trap while the older water washes away down the sewer line. New P-traps are installed into old sewer lines with threading compound, PVC adapters and cement.

P-traps stop sewer gases traveling into the bathroom area.
  1. With a reciprocating saw with a metal cutting blade, cut through the metal sewer pipe immediately on each side of the old drum trap. Remove the drum trap. The cut sewer pipes generally lead and attach to a male sewer pipe joint on one side, and a female sewer pipe joint on the other.

  2. Place a pipe wrench around the joint that one of the cut sewer pipes attach to, and turn the wrench handle counterclockwise to remove the sawed section of pipe from the joint. Remove the other cut sewer pipe on the other side of the drum trap in the same way.

  3. Brush threading compound around the thread of a PVC male adapter. Wrap single strand wicking around the threads. This will give extra protection to help prevent leaks. Screw the male PVC adapter by hand into the existing female pipe joint, and tighten it in place with an adjustable wrench.

  4. Brush threading compound around the threaded inside end of the PVC female adapter, as well as the existing male pipe joint it will screw onto. Also, wrap single strand wicking around the existing male pipe joint's threads. Screw the PVC female adapter onto the end of the existing male pipe joint by hand, and tighten it in place with the wrench.

  5. Insert the U-shaped bend of the P-trap into the end of the PVC female fitting (apply no PVC cement at this time). Measure from inside the inlet on the other end of the U-shaped bend with a tape measure to the inside of the inlet on the PVC male fitting. Cut a piece of PVC pipe to this length with a hacksaw, and scrape off all burrs with a utility knife. Insert this new PVC pipe section between the U-shaped bend and the PVC male fitting (no cement) to make sure it is the correct length.

  6. Remove the P-trap's bend and the new pipe section. Brush PVC cement around the inlets of the attached male and female fittings, as well as both ends of the P-trap's bend and both ends of the new PVC pipe section. Quickly push the trap's bend into the female inlet ---- one end of the new pipe section into the attached male fitting's inlet and the remaining end of the new pipe section into the other end of the P-trap's bend. Hold all joints to each other for 10 seconds while the cement starts to set.