Beginner with Plumbing here. I'm installing a dishwasher and I believe I'm working with a non-standard drain pipe (between two sinks) where I would like to connect a WYE fitting (to connect the dishwasher drain to).

When I was about to ABS cement the horizontal pipe shown I noticed that it fit loosely all the way through the 1 1/2" WYE fitting. I've never used ABS cement before but from videos I'd seen I assumed it shouldn't be loosely sliding through (around 3-5mm of wiggle room). Am I correct in believing this?

Then I found out that it could be an "old" pipe that would be 1 1/4" so I bought a 1 1/4" WYE fitting. This time the horizontal pipe was obviously much smaller than the larger "shoulders" of the WYE fitting and it just butted up against the narrow inner part of the WYE fitting. Again this didn't allow for a quarter turn whilst pushing-in-and-cementing...there was no snug fitting whatsoever.

Does anyone know what might be the issue? At this point I'm wondering if I've got some unusual outer diameter on the PP 1 1/2" pipe that I'm hoping to add the WYE fitting to. It does also look like "PP" means PolyPropylene...which I understand can't even be bonded with ABS cement. I suppose that makes sense since both ends of the pipe are compression fitting.

Ha, at this point I'm thinking I'm going to have to take the horizontal piece of pipe to the hardware store and say "how can I replace this so it accommodates a WYE fitting?"

Horizontal pipe is marked with PP 1 1/2 tubular f409

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