The kitchen drain pipe cracked in my old house so I decided to cut and replace with PVC.

Unfortunately the effective diameter of the pipe is about 2.5 inches which is slightly bigger than 2.4 inches for standard PVC pipe.

As a result, I could not fit it in the standard 2 inch coupling, even with a grease .

Looking for your help and maybe a proper product recommendations.

Thank you in advance

Here are the pictures of my pipe:

https://i.sstatic.net/ewmGG.jpg enter image description here enter image description here enter image description here enter image description here

  • 1
    Depending what type you used, the grease may not be compatible with the rubber, so you might want to clean it off well.
    – Ecnerwal
    Jan 23, 2022 at 19:51
  • De-burr the pipe you cut with a circular file.
    – Mazura
    Jan 24, 2022 at 14:07

3 Answers 3


You need a rubber coupling, since you have cast iron drain pipe which is sized differently than PVC, and even if it wasn't, a PVC coupling would never seal properly to the cast iron.

Rubber couplings are sometimes referred to as "Fernco's" which is one major brand of them.

One type has a metal sheild over the outside

Rubber coupling shielded image from menards.com

The other type just has clamps

Rubber coupling image from bestmaterials.com

A third option is one designed to insert into the cast-iron hub coupling if you completely remove the cracked cast-iron pipe from the lower section of pipe.

  • Considering the differences in size, I simply cannot connect the old pipe to this coupling. I bought exactly this one from HD. I guess the only option is to break the whole section ?
    – Andy
    Jan 23, 2022 at 21:58
  • Fernco connectors generally come in several varieties, you'll probably want on labelled CI (cast iron) to PVC. The pictured one is CI to Copper, which is sized differently (yet again) from PVC. I see one at HD that's "CI, PL (Plastic), ST (Steel) to CI, PL, ST", which is probably what you want.
    – atanamir
    Jan 29, 2022 at 5:03

You need to buy cast iron to PVC connectors. They make all kinds and sizes of adapters, you just need to know what you want to connect. Tell the guy, where you bought the adapter you have, exactly what you are trying to do and take a picture of it.

  • 1
    Unless, of course, the original item was purchased at the local big-box, in which case "Return the adapter, head to your nearest plumbing supply place, tell the guy..."
    – FreeMan
    Jan 24, 2022 at 15:56

I’m able to join pipes by heating the rubber part of the coupling. It becomes much more flexible then.enter image description here enter image description here enter image description here

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.