How to Repair a Cast Iron Drain Pipe

Written by peter h. crawford
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How to Repair a Cast Iron Drain Pipe
PVC pipes can fit into almost any area. (pipe fitting image by Joann Cooper from

All cast iron drain pipes eventually rust and need to be replaced. The ideal method is to use PVC pipes to replace them, as they will typically last much longer. In fact, they may never need to be replaced at all. The repair is not especially difficult, but it does require a few specific items to perform.

Skill level:

Things you need

  • Reciprocating saw with diamond tip
  • PVC replacement pipe (of similar size to existing pipe)
  • 2 no-hub bands with nut drivers
  • PVC glue
  • Tape measure

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  1. 1

    Turn off the water supply to the area you will be fixing.

  2. 2

    Locate the damaged or rotten area on the cast iron drain pipe beneath the sink. Mark off the area on each side to separate it from the cast iron that is still intact.

  3. 3

    Cut the rusted segment away with the reciprocating saw. Make two cuts: one just above and one just below the marked-off area. Remove the damaged pipe segment, and clean away the sludge and residue.

  4. 4

    Measure and cut a segment of PVC pipe to fit exactly into the cut out area. Fit it in as tightly as possible, using a small amount of PVC glue to seal the edges.

  5. 5

    Attach the no-hub bands to the areas where the PVC pipe meets the original cast iron pipe. The bands should wrap around the edge of both the PVC and the original pipe. Tighten the clamps of the bands by screwing in the nut drivers on the sides.

  6. 6

    Allow the PVC glue to dry before testing the pipe.

Tips and warnings

  • If your pipe leaks, you may need to reinstall the no hub bands or cut a new PVC pipe segment that fits better.
  • Make sure the pipe is completely dry when using the reciprocating saw. If water drips down into the saw, you run the risk of electrocution.

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