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I'm remodeling a bathroom and struggling to come up with the best way to hook into the existing drain pipe for my sink. Currently I have a 1-1/4" galvanized pipe with a couple of tees - one is capped and I assume is the original construction, the other is ABS from a previous owner's remodel, but has a couple potential of issues:

  • The ABS pipe used at the tee is 1-1/2" - there will be a pipe size reduction at the coupling that I assume could cause clogs.
  • The couplings used (Fernco Proflex, joining 1-1/2 to 1-1/4) appear to be rated at the 1-1/4" end for PVC only - if I understand correctly, they're not rated for the galvanized pipe at the end they're attached.

I'd like to cut out both tees and replace with a single ABS fitting. But I'm having a hard time finding appropriate parts:

  • I can't find ANY shielded couplings at the size. Flexible couplings are available but from what I understand they're not ideal for a behind-the-wall installation. Even if upsizing to 1-1/2 ABS, I can't track down shielded couplings rated for the galvanized pipe.
  • 1-1/4" ABS pipe and fittings don't seem to be something I can find locally, and even online are pretty scarce.

Replacing the entire vent pipe would involve tearing into basement walls, which I'm hoping to avoid.

Any other ideas on how to tackle this? Or leads on finding appropriate parts? Any help is appreciated!

Existing pipes Existing coupling

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OK, let's take this one step at a time...

It is unlikely pipe size reductions will cause clogs... impossible? No, but very unlikely.

The couplers are just flexible rubber connectors designed to join dissimilar/older piping to modern. I'm not sure exactly what it is you're seeing that has you concerned about the "rating", but we're just talking drain, right? So no pressure, no chemicals beyond normal cleaning. No worries.

FWIW here is what I'd do.

Unclamp your couplers. Don't cut, just remove the existing bits from the lower coupler (to galvanized pipe) to the upper T. Replace with PVC, re-use your couplers. Done.

Another point to just be aware of. Galvanized DOES corrode. It WILL eventually clog. The corrosion causes an irregular surface which WILL trap debris. This WILL eventually happen. Can't predict when as the variables are too great (your water quality/chemistry/hardness etc., what you send down that drain, cleaning chemcials etc.)

Good luck

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  • By 'rating' I'm referring to the manufacturers spec sheet - "Connects 1-1/2" CI, PL or St to 1-1/2" Copper or 1-1/4" PL". So if I'm reading that correctly, the coupling is not rated for steel at the 1-1/4" end. I don't doubt they'd hold up (already have for many years ...) just wondering if there's a more appropriate option out there.
    – Nick
    Jul 18, 2023 at 14:00
  • I guess a better way to phrase my question would have been something like - 'given generally available fittings, is there a better way to handle this than the previous remodelers approach?" Thanks for the help!
    – Nick
    Jul 18, 2023 at 14:05
  • OK. Full disclosure, not a licensed plumber here... remodel all my own stuff, do rentals etc. So to answer better, If the pic posted is what you want to know is there a better way... yes from the standpoint of remove the unnecessary stuff. I would not be concerned about using what you have there making mods as I described above.
    – STS1SS
    Jul 18, 2023 at 15:48
  • Makes sense. And good point about the galvanized corroding - given that, I doubt the small size reduction will be what ends up causing me issues. I think what I'll do is go with what you said, but potentially keep an access panel. That way if/when I get around to working in the basement I can replace the rest of the drain with 1.5 ABS up to the existing coupling. Thanks again!
    – Nick
    Jul 19, 2023 at 18:26

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