in a utility room at my home there is the water line and sewage line capped off bc they were not being used. What I want to do is add a utility sink in this location.

Cutting the water, cutting the cap, and throwing on a sharkbyte cut-off for the hot/cold water then running the water line from the sharkbyte to the hot/cold faucet is no problem to me.

What I am not sure how to do is set-up the plumbing for the sink drain. I assume it'll need a P-Trap, and I'll need to head to my local box store to pick up the supplies for that...but how do I "install" or "set-up" this plumbing?

The utility sink i purchased came with 1 1/2 pipes which connects no problem to the faucet that came with the sink...the issue I have is that the 1 1/2 plastic pipe fits completely inside of the pipe coming from the wall (image below) - what do I do here?

i keep getting an error trying to upload my image so here is a link


enter image description here

  • It'd help if you provided a sketch or picture. Obviously you'll need to know the diameter of the pipe (in the floor? wall?) and the sink tailpiece. If the pipe is in the wall, it's probably already vented. If the pipe is in the floor, you may want to add an AAV. Other than that, it's mostly a question of getting the fittings and lengths of pipe right.
    – Huesmann
    Commented Mar 19, 2023 at 12:25
  • @Huesmann - let me see if i can get you a good picture. It is already properly vented, and the pipe comes from the wall and has about 1 - 1.5 feet sticking out of the wall so I have plenty of "room" or "pipe" to work with. I have purchsed the sink i am going to put in, but I have not opened the box yet, so i'll need to look at pipe sizes. Is there no "special" way that you have to set-up the drain pipe? Commented Mar 19, 2023 at 14:12
  • Looks more like about 1-1.5 inches stuck out of the wall... What's the ID of the pipe, and of your sink's tailpiece?
    – Huesmann
    Commented Mar 20, 2023 at 12:01
  • @Huesmann - how would i get the id of the pipe? Commented Mar 20, 2023 at 13:41
  • You take a ruler and measure the Diameter on the Inside of the pipe.
    – Huesmann
    Commented Mar 21, 2023 at 12:33

2 Answers 2


A 1-1/2" pipe from a trap that fits completely inside a 1-1/2" pipe from the wall is...utterly normal.

Drain pipe and trap fittings are different actual sizes for the same nominal size. Or, you might have a 2" drain in the wall, still, it will be drain-pipe sized, and a trap adapter is available to fit that, too.

You need a trap adapter for the end of the wall pipe, which has a compression fitting that the (thinner wall, different relationship to nominal size) tailpiece from the trap gets clamped by (it's a slip fit, and then you screw it tight to seal)

One possibility is that you have a trap adapter sticking out of the wall (though your picture does not match your description of having 1-1.5 feet of pipe sticking out of the wall...) and simply need a new compression seal and compression nut. The other option is that what's sticking out is pipe thread (which will be a different size, and tapered if you look at it closely.)

  • seems like the crew that did the drywall got some plaster on the threading of the pipe. What is the easiest way to remove that? Sandpaper? Just try to screw on the "cap" and it'll clear out the grooves? Commented Mar 20, 2023 at 0:36
  • Neither. Scrape it out with a plastic or wooden tool (toothpick, expired credit card, etc.) Those should shift the drywall mud or plaster without damaging the threads. They should have bagged it before starting work (well, it should have been bagged anyway for the sewer gas issue, if not capped.)
    – Ecnerwal
    Commented Mar 20, 2023 at 1:24
  • Wire brush works a lot faster than a toothpick, etc.
    – Huesmann
    Commented Mar 20, 2023 at 12:00

It's hard to tell because it seems to be covered in paint but is that a threaded connector in the wall? If you buy a complete P-trap kit with a horizontal arm, the arm is meant to fit inside that pipe and should include a compression nut to fit that thread. If that's a thread.

There are LOTS of youtube videos on how to do this. It's better to get an overview from there, take a stab at it, and come here to solve specific problems.

Meanwhile you should cover the drain to prevent sewer gases in your room. A sandwich bag and a rubber band will do.

If you've never fitted a drain basket to a sink before, that's a little more involved, not quite as obvious or mechanical as the trap connections. Also easily learned on youtube and with some trial and error ... so keep a bucket underneath the sink :)

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