How to Move a Cast Iron Toilet Drain


Cast iron sewer pipes are common in many older homes. Cast iron was preferred as a drainpipe material for its long lifespan and rugged construction. If you plan to move your toilet's location, the drain into which it empties will also have to be moved. Cast iron is typically cemented together and may prove difficult, if not impossible, to remove without cutting into it. The process of moving a cast iron toilet drain requires some plumbing skills and a few specialized tools and materials.

Things You'll Need

  • Wrench
  • Bucket
  • Handheld drill
  • Hole cutter bit
  • Oversize pipe wrench
  • Pipe cutter
  • PVC cleaner
  • PVC cement
  • Double female PVC adapter
  • PVC piping
  • PVC elbows
  • PVC adapters
  • Hacksaw
  • Metal pipe mounting brackets
  • Screw gun
  • Wood screws
  • 90-degree PVC elbow
  • New flange
  • New wax ring
  • Turn off the water supply shutoff valve behind the toilet. Flush the toilet until the tank is empty. Use a wrench to loosen and remove the water supply line from the underside of the toilet tank. Place a bucket under the supply line opening to catch any remaining water.

  • Locate the two bolts on either side of the bottom of the toilet base that hold the tank in place above it. Loosen the bolts, lift the tank off the base and set it aside. Detach the toilet from the floor by removing the two bolts at either side of the base. Use a wrench to turn the nuts in a counterclockwise direction to loosen them. Lift the toilet base from the floor to access the drain beneath.

  • Mark the new location of your toilet and make a pilot hole through the floor with a handheld drill. Move to the floor below and check that there are no floor joists, wires, pipes or other structural impediments to the new location. If not, equip the drill with a hole cutter bit and make a hole that matches the requirements of the new toilet flange you plan to install.

  • Move to the floor below where the cast iron toilet drainpipe is visible and accessible. Locate the nearest pipe joint to the toilet end of the drain system. If the pipe is threaded and in good shape, use an oversize pipe wrench to loosen it. If the pipe is old, cemented together or otherwise cannot be loosened, use a large pipe cutter to make a cut in a straight length of cast iron pipe most easily accessible to you and most convenient to the relocation site for the toilet.

  • Make another cut just below the toilet flange, which is still mounted in the floor at the old toilet location. Remove the pipe you cut and remove the flange by lifting them up and out from above. Install PVC pipe that is the same diameter as the existing cast iron pipe to redirect the drain to its new location.

  • Clean the open rim of the cast iron pipe with PVC cleaner. Apply PVC cement to the open end and to one end of a double female adapter of the appropriate size then slide that end over and onto the cast iron pipe. Install a combination of straight pipes, elbows and adapters to route the drainpipe to the intended toilet location. Follow the same cleaning and cementing method as described and use a hacksaw to cut the pipes to fit.

  • Suspend the PVC piping from the floor joists above with metal pipe hanger brackets. Use a screw gun and wood screws to fasten the brackets into place. Space one bracket every 2 to 3 feet. Slope the pipe downward slightly from the toilet location to the cast iron pipe.

  • Attach a 90-degree PVC elbow directly below the toilet's new installation location so that the drainpipe faces upward toward the flooring surface above. Install a piece of straight pipe onto the elbow so it extends to the level of the flooring surface. Move to the bathroom upstairs and slide a new flange into position over the drainpipe in the toilet's new drain opening. Use PVC cement and mounting screws to fasten the flange in place.

  • Place a new wax ring into position then install the toilet onto the new flange. Tighten the toilet base mounting bolts then reinstall the toilet tank and the water supply line. Open the water supply shutoff valve and test the toilet.

Tips & Warnings

  • PVC piping is cheaper, easier to work with and longer lasting than cast iron. It is the standard in new homes today and should be used to replace old drain lines whenever necessary.
  • Refer to the manufacturer's specifications for your particular toilet model to make sure the plumbing you install and the drain location match the requirements.
  • Never attempt plumbing work which is beyond your capabilities. Serious damage and flooding can result. Call in the professionals for the big jobs.

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