How to Connect PVC to a Cast Iron Soil Stack

Written by david young
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How to Connect PVC to a Cast Iron Soil Stack
You can join PVC and cast iron pipe with a flexible union. (Comstock/Comstock/Getty Images)

Whether you're remodelling a single room or retrofitting an entire house, there may come a time when you have to join newer PVC pipe with older cast iron sewer lines. Cast iron was once a common material for sewer lines and is still present in many older homes. When remodelling, PVC is a popular choice due to its light weight, low cost and easy installation. Joining PVC to cast iron is also easy with the use of flexible couplings.

Skill level:
Moderately Easy

Things you need

  • Nut driver
  • Flexible coupling

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  1. 1

    Turn the clamp nuts on flexible coupling counterclockwise until the coupling is loose enough to fit over the largest diameter pipe.

  2. 2

    Slide the coupling over the end of the smaller diameter pipe. Slide the coupling up the pipe until it is flush with the end of the pipe.

  3. 3

    Line up the ends of the two pipes. Slide the coupling until it sits halfway on each pipe with at least a 1-inch overlap on the pipes.

  4. 4

    Turn the nuts on the clamp clockwise until the coupling is firmly attached to both pipes.

  5. 5

    Run clean water through the pipes while checking for leaks. Continue tightening the clamp nuts until all leaks stop.

Tips and warnings

  • Flexible rubber couplings are not approved in all areas. Check with your local codes before installing one.

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