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I need to extend some 4" PVC drainage pipe. The problem I'm having is that the existing pipe is "Type C" ("tele-duct"). It has a slightly different outer diameter (4.350") than a typical PVC pipe (e.g. Schedule 40, 4.50").

I've only been able to find one possible "Type C to Schedule 40" adapter product, and it's from a wholesaler with a high minimum purchase. Is there any way to wrap the existing pipe with some kind of sheathing to increase the outer diameter before cementing it to a "normal" Schedule 40 fitting?

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    Is digging out the existing drain pipe an option? Because what you have isn't drain pipe. It's conduit for wires.
    – longneck
    Commented May 26, 2020 at 4:02
  • @longneck: No. I mean, of course I could redo what already exists, but it's not worth the expense. (It's probably at least 50 feet of pipe under my backyard.) Yes, I already asked myself, "why did the idiots who put this in use telephone conduit?"
    – user1071847
    Commented May 26, 2020 at 6:31

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Cast iron has roughly the same O.D. as your Type C. You could use a shielded "no hub" connector for iron to PVC, such as the Fernco 3000-44.

You could also go all bushcraft and stretch your Type C a bit. By heating it slowly and carefully you'll get it soft, then work a sphere or cylinder of the right size into it until it cools. You can then do a standard PVC coupler.

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