How to Install a Fernco PVC Cast Iron Adapter

While older houses often have sewer lines made of clay, lead or cast iron, most newer homes' sewer lines are made of either black ABS plastic or white/gray PVC. After cutting both the cast iron and PVC pipe to the required length, a Fernco coupling adaptor is used to join the two together. This coupling is made of flexible rubber and tightens to the pipes with metal hose clamps to create a water-tight seal.

Install a Fernco PVC Cast Iron Adapter
  1. Mark the cast iron sewer pipe in the place where the PVC sewer pipe will be attached. Wrap the chain of a snap cutter squarely around the pipe, resting the chain on the mark. With the cutter's handles open, attach the closest chain link to the hook on the end of one of the handles. Quickly pull the cutter's handles together. This will create a clean straight break right through the pipe. Remove the cutter and cut the unwanted section of cast iron pipe into movable lengths. Remove all sections of unwanted cast iron pipe.

  2. Measure and mark the PVC sewer pipe to the required length. Make a straight perpendicular cut through the pipe at the mark using a miter saw. Scrape off all plastic burrs from the pipe end with a utility knife.

  3. Mix together some soapy water. Apply it with a brush around the outside end of the existing cast iron pipe. Push the Fernco coupling halfway onto the end of the pipe.

  4. Apply some soapy water around one outside end of the section of PVC sewer pipe that needs to be attached to the cast iron pipe. Push the PVC pipe into the other end of the Fernco coupling. Make sure the coupling is positioned half way on the cast iron pipe, and half way on the PVC pipe.

  5. Tighten the metal hose clamps surrounding each end of the Fernco coupling to 60 inch-pounds of torque, using a screwdriver.


  • Wear eye protection when sawing through the PVC pipe and when using the snap cutter.