How to loosen a cast iron clean out plug

Written by kenneth crawford
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How to loosen a cast iron clean out plug
(Hemera Technologies/ Images)

Many older homes still have old cast iron drain and sewer pipes rather than the PVC plastic pipes used in modern home construction. The end of the drain pipe has a removable cap plug. This plug allows access to the drain pipe for removing clogs and other obstructions. Cast iron has a tendency to rust, so drainpipe plugs that have not been removed in some time may seem moulded to the pipe by rust. Loosening a cast iron clean-out plug from a drainpipe requires softening the rust enough to break it free.

Skill level:
Moderately Easy

Things you need

  • Penetrating lubricant
  • Steel wire brush
  • Pipe wrench
  • Mallet

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  1. 1

    Spray the perimeter of the cast iron clean-out plug with penetrating lubricant. Spray the seam between the plug and the inside of the cast iron pipe. Allow the penetrating lubricant to work for 30 minutes.

  2. 2

    Scrub the seam between the plug and the pipe with a steel wire brush. The lubricant softens and cuts through the rust and the wire brush helps to dislodge the rust further.

  3. 3

    Adjust the jaws of a pipe wrench around the protruding square peg on the end of the plug with the handle of the wrench pointing to the left.

  4. 4

    Tap the top pipe-wrench handle with a mallet while holding the wrench on the square peg to begin turning the drain plug counterclockwise. Once the cast iron clean-out plug begins to turn, continue turning it with the wrench until it is out of the drainpipe.

Tips and warnings

  • If the plug does not begin to move after tapping the wrench handle several times, spray more lubricant into the seam and wait another 30 minutes.

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