The best way to replace a sanitary tee (for a bathroom sink) given existing 1-1/4″ galvanized drain/vent pipe

absbathroomdrainplumbingvent

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

Best Answer

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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