PVC to cast iron

[Keith]

I've coupled PVC to old (unaccessible) lead drain pipe and to cracked/cut cast iron drains, but now I'm on a new project in my new house. I have cast iron in the basement, and along the way there are a few y's with the hex- nut screw cap on them.

I'd like to remove one of those caps and use PVC to tie in a new 2" drain for my kitchen- the old drain is (at best) 2" iron and barely drains at all; and it is inaccessible, so I'd just cap it under the kitchen sink and run the new PVC in from another direction and up in the original location.

However, before I take the cap off the cast iron, I'd better ask...I'm guessing that a standard threaded PVC coupling isn't going to fit the threads on the cast iron (at least not with any type of effective seal). What is the preferred method of making this type of junction? I can use a rubber coupling again, although I don't have enough length of iron pipe to cut it, so it would be over the large end where the cap sits, and I'm not sure if a rubber coupling would have enough room to seat well.

Thanks for your suggestions, Keith

[Bert Byfield]

Replace enough iron with plastic until all you have left is simple pipe-to- pipe connections, which will connect with the rubber couplings. The iron is likely old and going to make more trouble, so the less of it the better.

[Sev]

I would screw in a cast iron male-to-female adapter(with pipe dope) after removing the cap, then put the pvc in this with a lot of the gray stuff- think it's called 'plastic weld' making sure pvc is clamped well enough that it will not move.

[Bert Byfield]

That would probably work, but the mechanical solution (rubber coupling) is better in my opinion. It works, and it's less messy.

[Sev]

Reason I suggested it was he said he wasn't sure he had enough room on the Y to attach rubber coupling.

[hallerb]

if noise matters cast iron is quiet, plastic conducts noise really well.