I just had a plumber repair my 4" waste line, which was cast iron.

He replaced a 10' section with ABS.

At the end that transitioned from ABS to Cast Iron he used a coupling specifically designed for that (part # 3000-44, labelled '4" Cast Iron to 4" Plastic" - see first photo). However at the Cast Iron to ABS transition it appears he used a regular no-hub coupling (see second photo). (My reference direction is the direction of water flowing downhill).

I tried to ask him why, but I didnt get an answer. I want to give him the benefit of the doubt, but I also want a fix that doesnt fail early.

Question: is there any reason why one would use a '4" Cast Iron to 4" Plastic" coupling at the 'ABS to cast iron' joint, but not at the 'cast iron to ABS' joint?

It's possible I'm mis-identifying the connector on the 'cast iron to ABS' joint - see photo below. That's not a "CI to PL" coupling, right?


CI to PL coupling

other coupling

  • 1
    Please show what's at the other end. From your description you seem to indicate that the same type of coupling is used at both ends.
    – jwh20
    Feb 9, 2022 at 11:04
  • 1
    Consider adding a bit of light to the other picture. Also another picture to show context in addition to the details would be helpful.
    – FreeMan
    Feb 9, 2022 at 14:08
  • 1
    No-hub connections tend to be made when the pipes can't be separated or rotated. Are the two situations actually different in that regard?
    – isherwood
    Feb 9, 2022 at 14:14
  • 5
    My guess is that's what they had on hand.
    – isherwood
    Feb 9, 2022 at 17:39
  • 1
    The one with the yellow label is not a "cast-iron to plastic fitting" It's a "cast iron to plastic, steel, or no-hub cast iron" fitting, per its own labeling. These are different versions of the same thing.
    – Ecnerwal
    Feb 10, 2022 at 0:43

1 Answer 1


It's a shielded (stainless wrap, above-ground use only, aids in shear force) rubber coupling.

Part description for one such item states:

Compatible with Sch. 40 PVC, cast-iron, plastic, steel, copper and tubular DWV pipe

So basically everything you are likely to find as 4" drain pipe.

Unclear what you are upset about. If it's not being buried in the ground it's entirely suitable for the job it's doing.

  • Thanks. I'm not upset, just trying to understand why at one transition he used a coupling specifically designed for CI->PL, but at the other end he did not. I'm assuming there is a good reason, and trying to find out what it is.
    – tom
    Feb 9, 2022 at 18:20
  • 1
    @tom It's probably what he had on the truck at the time. Many different companies making the same type of part. Don't lose sleep over this.
    – JACK
    Feb 9, 2022 at 18:55
  • If it doesn't leak it's good. One of them does the job. The other one is specifically designed and marketed for the job. But that doesn't mean that "does the job" doesn't do the job. Obviously. As long as they don't leak and the two cast iron ends are well supported near the two hubs, you are fine. If the supports are distant he should have added a couple near the hubs. If he would have had to come back another day to finish the job because he couldn't get two identical couplings you would have had good reason to question that decision.
    – jay613
    Feb 9, 2022 at 18:58
  • Thanks both - that's useful. It's supported 4" from the end that uses the regular coupling, and 26" from the end that uses the special CI->PL coupling.
    – tom
    Feb 9, 2022 at 19:48

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