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Converting a tub to a shower, and with the drain location changing I'm just getting back to the underbelly and seeing the alignment of things before hooking it all back up.

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You can see the new drain now sits into the room roughly 1.5-2in as compared to the max reach of the new p-trap. I put a piece of 2in into the drain to illustrate the shift. Side note, I do realize I will be transitioning from 2 to 1.5in, which is OK per code and flow rate of the shower head in my area.

I was hoping the extra pipe going to the p-trap was going to be the place to splice in, but now I'm not sure. Should I be rebuilding everything between the lines? Playing around with elbows to get it over to the new drain?

I'm comfortable working with ABS - just want to be sure it's the best approach.

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  • Do my eyes deceive me or are you feeding the new trap into a sani-T with the 'leg' pointing down into the old trap?
    – brhans
    Sep 23 '20 at 13:23
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You should cut the 2" main line (at the location shown in the first picture) and rebuild the assembly entirely, eliminating the combi (reducing tee) and any 1 1/2" components and orienting a new 2" sanitary tee to the correct angle to line up with a new 2" trap located directly under the shower drain. Why on earth would you reduce to 1 1/2" here when you could very easily make this all 2"?

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    Yes! Not the place to "save" $10 on fittings.
    – Ecnerwal
    Sep 23 '20 at 11:51
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    If I wasn't needing the eliminate and rebuild, I didn't see any harm in it? Given the need to rebuild, though, I will go with the 2" to the assembly. Makes sense, and saving a few bucks here isn't a driving force @Ecnerwal. Thanks for clarifying!
    – CFA
    Sep 23 '20 at 13:17
  • A 1.5" pipe is barely over half the size (area, capacity) of a 2" pipe. 56.25% if you want to get picky. Thus, a 2" trap is one heck of a lot harder to clog than a 1.5" trap, even if your local code permits. Since most (all?) shower drains are 2" drains, under ICC (which I have to work with, subject to my local modifications) I think it would be caught by the "you can't reduce the size of a drain" rule, but I may be interpreting too strictly, or I may not have looked for 1.5" shower drains.
    – Ecnerwal
    Sep 23 '20 at 13:24
  • For sure. I look forward to the flow with the 2" setup, then! Thanks for your thoughts.
    – CFA
    Sep 23 '20 at 14:55

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