I have an open 1.5" drain pipe in the wall. I just need to redirect it through the (currently non-existing) drywall and put in a trap. What is the proper way to do this? Do I just put a 90 degree EL on the pipe?

Also, I noticed that most traps are 1.25" instead of the 1.5" of drain pipe that I have. Do I just step my drain from 1.25" to 1.5" and call it a day or is there some special way to do this properly?

Is PVC or some other material preferred? What else do I need to take into consideration?

  • Is the drain pipe vented already? A picture would help.
    – Comintern
    Commented Aug 3, 2014 at 15:45
  • @Comintern Yes it is vented Commented Aug 3, 2014 at 16:35

2 Answers 2


There are many ways to assemble the new drain. Assuming the 1 1/2" pipe is threaded:

1) screw an 1 1/2" ABS female adapter to the pipe.

2) using a short piece of 1 1/2" ABS pipe, glue an 1 1/2" ABS slip X slip elbow on, so it ends up facing out towards where the new trap will be.

3) glue a piece of 1 1/2" ABS pipe of appropriate length into the elbow (longer is better, you will be cutting this back later). This will be the pipe that protrudes through the drywall.

4) install drywall.

5) buy an 1 1/2" ABS P-Trap assembly, the "slip-joint" type (it will come in a complete kit).

6) install bathroom sink.

7) pre-assemble and dry fit everything, measure 3 times, cut once!

8) cut 1 1/2" abs pipe back and glue on the 1/1/2" ABS male adapter that came with the P-Trap kit.

9) assemble P-trap and adjust to fit. Your sink drain pipe (tailpiece) may be 1 1/4" but the P-trap kit comes with reducing nuts/washers to accommodate.

10) have rewarding beer for job well done. No leaks = no worries.

  • 1
    The 1 1/2" pipe is simply an open PVC pipe (I put it there). It doesn't have anything glued to it yet Commented Aug 3, 2014 at 16:58
  • Is it black? If so it is ABS. If it is white it is PVC. ABS is normally used for sewer/drain pipe. If it is normal pipe size (as opposed to "tube size", which is measured on the outside diameter, or O.D.) you can glue a ABS slip X slip elbow to it and skip the female adapter. You will need special glue to join PVC to ABS (it's called Universal Cement), if that is the case as they are different type plastics. Commented Aug 3, 2014 at 20:55
  • It's regular schedule 40 PVC (white). It is what was used as my main stack so I used it for the rest of the plumbing Commented Aug 3, 2014 at 20:59
  • That's OK, now that it is there just use the universal glue and continue as described Commented Aug 3, 2014 at 23:28
  • Would you mind linking a picture of each of the pieces you mentioned? Commented Aug 4, 2014 at 1:12

1 1/2" ABS P-Trap kit

1 1/2" ABS slip X slip elbow

slip joint style fitting, do not use these fitting inside the wall, ever.

universal (or "all purpose") glue, make sure it says PVC and ABS

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