I am trying to remove a cast iron plug from a cast iron drainage clean out behind the bathroom in an 80-90 year old apartment building to unclog the drainage. The plug is so tightly set that despite heating with a torch and liberal applications of WD-40, use of a big pipe wrench and a lot of elbow grease, I am not able to budge it. Any and all ideas how to undo the plug would be appreciated.

Hi PIN

If a big wrench hasn't worked then you could try a bigger wrench... like a 2 foot wrench. A wrench that size, however, can actually spin the head of the plug clean off so be careful.

If that doesn't work then the next step to try would be to use a cold chisel and hammer to remove the plug. Here, using the hammer/cold chisel, you kind of cut a v groove into the left side of the plug threads and then set the chisel into the v groove and hit it real hard with the hammer... should loosen the plug up. Once you loosen it even a little bit try the wrench to finish removing the plug.

Finally, if that fails to work, you want to cut the head of the plug off (or twist it off using that big wrench) and then using a reciprocating saw with a metal blade cut an X through the hole toward the threaded edges and then cave/wiggle the plug inward/outward being sure NOT to drop any of the pieces into the pipe and also being sure NOT to cut into or damage the cast iron threads, right (see image)?

Remember, brass is a soft metal and should be pretty easy to get out... just need lots of patience here!

If you end up cutting the plug out or damaging it in such a way that the plug isn't reusable then take the plug parts with you to a local plumbing supply store as there are many different size brass plugs for cast iron.

When you install the new plug purchase a little plumber's grease and grease the plug real good so the next time this happens it will be easy to remove.

Good luck!

Mark

Mark gave you some excellent solutions but the first thing I try to do is loosen the plug by impact. Put a 18"b pipe wrench on that cast iron plug and hit it with a heavy hammer. Once loosened it should be easy to turn out. Good luck, Tom