I have a cast iron y connection in my 4" waste stack. The former owners used the Y to plumb a bathroom but thier work was very substandard. I pulled all their plumbing and ran a new waste line for the bathroom. My problem is their old y connection is completely broken (the pipe that was originally installed is broken off flush with the "y" hub) and I can't find a way to cap it. I found a threaded lead cap at the hardware store that is labeled "universal cap". Is this something I can thread into the broken pipe that is in the y valve? Is there any other details or methods to blocking this hole?

Thanks

". I found a threaded lead cap at the hardware store that is labeled "universal cap"."
No, You will notice the cap
's tapered. The cap is meant to thread into a old clean out that has female threads that are too worn to engage a regular threaded cap.

The cast iron pipe that's broken off in the wye has a lead and oakum joint that can be removed by melting it out with a torch.
Once the old pipe, lead and oakum's cleared away a 4" clean out can be installed in the wye using a DuelTite Gasket,(see image) or by pouring and caulking in another lead jioint. Good luck, Tom

Not exactly the answer I was looking for since it's tight quarters and a torch in there sounds like a recipe for a fire, but I appreciate understanding the problem better.

But here's a follow up: Isn't the foul odored gas eminating from this fitting potentially flammable or is that just a myth?

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Originally Posted by dsjunk

Not exactly the answer I was looking for since it's tight quarters and a torch in there sounds like a recipe for a fire, but I appreciate understanding the problem better.

But here's a follow up: Isn't the foul odored gas eminating from this fitting potentially flammable or is that just a myth?

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OK, then let me give you you another option. Drive a screwdriver down through the lead until it's split. Now begain to lever the lead ring up and out. Keep prying the lead up until it comes out and then clear out the old pipe and oakukm. You may now install a DuelTite Gasket and a 4" cast iron clean out. If you need instructions on installing DuelTite Gaskets let me know.
To answer your question, the methane content of sewer gas makes it explosive. Good luck, Tom