How to Replace Old Cast-Iron Drain Pipes

Updated February 21, 2017

The assault of water and waste causes cast-iron drain pipes to deteriorate, leaving homeowners with a mess and an inefficient drain system. Fortunately, replacing old cast-iron drain pipes is a project within the capabilities of a beginning plumber. With the proper tools, the right materials and attention to detail, you can replace your old cast-iron drain pipes and renew your home’s drain system.

Remove old, deteriorated portions of cast-iron drain pipe. Use a reciprocal saw equipped with a metal cutting blade to cut through the pipes. Locate a position on the old pipes that is free of rust and generally sound. Create a clean cut straight across the pipe. If a reciprocal saw cannot access the pipe, use a hacksaw to cut the pipe by hand. Use a file and emery cloth to smooth the cut edge. Run the file and emery cloth around the pipe to remove burrs. Wipe metal shavings from the pipe with a lint-free cloth.

Measure the diameter of the old pipe and the new pipe, using a tape measure. Use a flexible rubber connector that accepts the old pipe’s diameter on one side and the new pipe’s diameter on the other. Use a flathead screwdriver to loosen the clamps on both sides of the connector. Stick the screwdriver’s blade into the clamp’s slot and twist counterclockwise to loosen.

Attach the flexible rubber connector to the old pipe. Slide the corresponding side of the connector over and onto the old pipe. Shimmy and twist the connector to overcome stickiness or a tight fit. When the connector extends approximately halfway over the old pipe, tighten the clamp that rests over the pipe. Insert a screwdriver into the clamp’s slot and turn clockwise to tighten.

Insert a new drain pipe into the open side of the flexible connector. Shimmy and twist the new pipe until it extends halfway into the connector or butts against the old pipe. Hold the new pipe in place, insert a screwdriver into its clamp and turn clockwise to tighten.

Wrap plumber’s tape around the new pipe. Position the plumber’s tape as close as possible to the new connection. Stick a screw through two of the tape’s holes and load the screw onto a drill. Pull the plumber’s tape taut and fasten the screw to a framing member, such as a wall stud, using fasteners.


Replace old cast-iron pipes with ABS for a long-lasting drain system. Flexible rubber connectors are available in 90-degree angles, tees and more--choose the best fitting for the job. Consider renting a chain-type iron pipe cutter--it creates less stress on the pipe and requires only muscle power.


Wear goggles and gloves when cutting cast-iron drain pipes. Always check local plumbing codes before starting a project.

Things You'll Need

  • Tape measure
  • Reciprocal saw
  • Metal-cutting blade
  • Hacksaw
  • File
  • Emery cloth
  • Lint-free rag
  • Flexible rubber connectors
  • Flathead screwdriver
  • Plumber’s tape
  • Drill
  • Fasteners
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About the Author

Based in Hawaii, Shane Grey began writing professionally in 2004. He draws on his construction experience to write instructional home and garden articles. In addition to freelance work, Grey has held a position as an in-house copywriter for an online retailer. He holds a Bachelor of Arts in theater arts from Humboldt State University.