How To Replace A Tub Drum Trap With A PVC P-Trap

Drum traps are commonly plumbing fixtures found on the tub sewer line  in older homes. Similar to a P-trap, the drum trap prevents sewer gases from entering the home.

However, in modern home, legal codes require P-traps, since they are self-cleaning. Drum traps have to be maintained, since they don't clean themselves, and you may find them clogged. The ideal solution is to install a P-trap, which you can do yourself, by following this guide.

Gather Materials to Replace the Trap

To convert the drum trap, you need:

  • work gloves
  • safety glasses
  • step-ladder
  • tape measure
  • rags
  • pliers
  • bowl or bucket
  • utility knife
  • pipe dope
  • PVC cement
  • sandpaper
  • single-strand wicking
  • reciprocating saw and metal cutting blade
  • PVC female or male adapter
  • PVC P-trap

Ensure all the water has been drained from the tub and shut off the house water supply from the water meter. Locate the drum trap, which is commonly a visible box-shaped cast iron pipe on the ceiling under the tub.

Sometimes, you only see the cap from the floor. It is easier to work from below the trap instead do having to remove flooring.

Remove the Trap

Set a bucket under the trap to catch water when you remove it. Look for the trap connectors or nuts, which is where you start cutting. Place a step-ladder to reach the trap, if needed. Use the saw to cut through the points of the connectors on each side of the trap. 

Remove the trap, and set it aside. The cut pipes commonly attach to a male sewer pipe joint. Detach the joint on the threaded adapter on the cut section with the wrench by turning it to the right. You may need to use another wrench to hold the hold the pipe while you turn the nut.

Install the New P-Trap

Spread pipe dope on the existing  PVC male threads and female adapter threads, then wrap it with single strand wicking to protect the fittings against leaks, Attach the female adapter onto the male adapter, slide the U-part of the trap into the female fitting, but don't add pipe cement yet.

Measure the length between the inlet opposite the U-shaped portion and the PVC male pipe fitting, cut the extension pipe to fit. Smooth burrs with sandpaper or cut them using a utility knife.

Test fit the pipe and trap before you install it, and test the fit of the pipe between the U-shaped section. If everything fits, spread pipe dope over the new male and female fitting and P-trap ends.

Immediately insert the P-trap bend into the female inlet, the free end into the male inlet. Attach the extension pipe into the other end of the trap; tightening connections with a wrench, then insert additional elbows, if needed. Cover the connections with pipe cement, press the pipes together several seconds with your hands to help the cement seal, and let it dry. Contact a service, like Quality Plumbing, for more help.