There's a cleanout plug on this pipe that I simply can't get loose. I've tried liquid wrench, PB blaster, heating up the area with a torch, everything I can think of. All that's really left is to go after the plug with a drill and a saw and just pull it apart. However, none of my local hardware stores HAVE any 4 inch cast iron, all they have is PVC. Can I put a PVC cleanout plug in a Cast Iron cleanout?

4 Answers 4


Yes, it should be no problem. Just use teflon tape on the threads to seal it.

I would worry though if you can't get the plug out, that the threads in the pipe won't be any good (or you'll destroy them in the process of attempting to get the plug out). If that happens, you'll need to re-thread the pipe. You should be able to rent a tool for this at your local tool rental place.

You don't mention what the pipe is, so just be prepared that you may not be able to use it until it's repaired, if you do have a problem with the threads.

  • Its the stack for the upstairs bathroom, but it's upstream and above the stack for the downstairs bathroom. I'm thinking that the best way to pull the old plug is going to be to drill/cut near the edge and pull out the center, then try to heat/break the remaining ring.
    – philosodad
    Nov 5, 2010 at 14:58
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    You'll want to stock up on drill bits -- cast iron is hard stuff. Nov 5, 2010 at 15:13

Another option would be to cut the pipe above and below the cleanout, and install a PVC Y-fitting with a cleanout cap using no-hub couplings like these:

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I would think that drilling and/or sawing out the old cast iron cap is going to be a giant pain in the rear, and will be likely to damage the cleanout fitting to the point where it needs to be replaced anyway.

Make sure your cast iron stack is supported above before you cut it.

  • What tools would I need to cut out the old pipe?
    – philosodad
    Nov 5, 2010 at 14:55
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    I'd recommend renting a snap cutter like this: plumbingsupply.com/snapcutters.html. If you have a reciprocating saw, you can buy special grit blades for cutting cast iron as well, but the snap cutter will be a lot quicker. Nov 5, 2010 at 15:10
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    @Aww, crap. that's what I get for not reading thoroughly. Sorry about that.
    – Doresoom
    Nov 5, 2010 at 20:30
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    No problem! I've certainly had my share of those on here too... Nov 6, 2010 at 1:57
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    I ended up having to cut the pipe, something further downstream got damaged--the original install was a major kludge job--so I had to replace more iron anyway. The grit blade/reciprocating saw took 5-10 minutes a cut, but it was a long 10 minutes.
    – philosodad
    Nov 9, 2010 at 1:11

Hole saw out the center and cut a pie shaped piece out with a saws all all the way to the threads but not into the threads, then with a hammer and punch knock out the pie shaped piece and remove the rest with channel lock pliers. Do it every day as a professional plumber. And if the threads are different stop at a local plumbing outfit and get a lead plug.


Another options to the PVC one, in case the threads are damanged or the thread count doesn't match up, would be to use an expansion plug:

(I couldn't get the right size for mine at the local store, so I had to also cut down a rubber coupler to make it a closer match to the inner diameter)

  • I doubt using a test plug will meet code but if you use one of the sturdy metal plugs it will probably work fine.
    – auujay
    Oct 19, 2012 at 14:47
  • @auujay maybe not, but surprisingly when I had a home inspection, they misses that the cleanout was covered in duct tape ... when I removed it later, I found someone had shoved a plastic cup in there, then put a plastic bag over the whole thing + layer of duct tape.
    – Joe
    Oct 19, 2012 at 15:18

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