• In this video, This Old House plumbing and heating expert Richard Trethewey shows how to replace an old bathtub drum trap with a new PVC P-trap.

    Steps:

    1. Use reciprocating saw fitted with a metal-cutting blade to cut out the old iron drum trap; be careful when lowering the trap, it's filled with water.

    2. Loosen the old threaded adapter that's attached to the existing drain line using two large pipe wrenches; use one wrench to hold the pipe, and the other to turn the adapter.

    3. Once it's loose, remove the adapter with pliers.

    4. Brush pipe dope onto the threads of a PVC male adapter, then wrap the threads with single-strand wicking to provide extra protection against water leaks.

    5. Insert male adapter into the existing iron fitting, and tighten the adapter with pliers.

    6. Apply pipe dope and wicking to the existing iron male fitting, then install a threaded PVC female adapter, tightening it with pliers.

    7. Dry fit (no glue) the PVC P-trap and PVC pipes to ensure they fit together properly.

    8. Measure last piece of PVC pipe, and cut it to size using a PVC cutter or hacksaw.

    9. Use a pocketknife to scrape off any rough burrs from the just-cut end of the PVC pipe.

    10. Dry fit together all the parts one final time, then use an indelible marker to draw alignment marks onto the pipes and fittings.

    11. Disassemble the PVC pipes and fittings, then clean them with PVC primer.

    12. Permanently glue together the pipes and fittings with PVC cement, making sure you line up the marks drawn earlier in Step 10.
    • Difficulty: Moderate
      Requires basic plumbing skills and working in cramped quarters.
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    Selected Topic/Section

      Tools List

      • reciprocating saw
        Reciprocating saw fitted with metal-cutting blade
      • pipe wrench
        Pipe wrench, two large wrenches needed to disassemble the old iron pipe and trap
      • pvc pipe cutter
        PVC pipe cutter or hacksaw, used to cut pipe to length
      • tongue-and-groove pliers
        Pliers
      • 30-foot tape measure
        Tape measure
      • permanent marker
        Indelible marker, for marking the alignment of PVC pipes and fittings prior to gluing
      • pocket knife
        Pocketknife, used to remove rough burrs from the ends of just-cut PVC pipe.

      Shopping List

      1. PVC P-trap used to replace existing iron drum trap

      2. 1½-inch PVC pipe

      3. 45° and 90° PVC elbows

      4. Threaded PVC male adapter used to connect to existing iron pipe

      5. Threaded PVC female adapter used to connect to existing iron pipe6. Pipe dope for creating a watertight seal on threaded PVC fittings

      7. Single-strand wicking used to help seal threaded connections between PVC and iron fittings

      8. PVC primer and cement for gluing together PVC pipes and fittings

      9. Bucket to catch drips and empty water from old drum trap