How to Connect PVC to a Cast Iron Soil Stack

You can join PVC and cast iron pipe with a flexible union.
You can join PVC and cast iron pipe with a flexible union. (Image: Comstock/Comstock/Getty Images)

Whether you're remodeling 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 remodeling, 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.

Things You'll Need

  • Nut driver
  • Flexible coupling

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

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.

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.

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

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

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