[Clearer picture with all the drains][1]I am planning to finish my basement. When I bought the house they said it is roughed in for a full bathroom, but I'm unable to figure out what the drain pipes are.

My guess is the right one is for sink, center one if for toilet and the left one is for shower but the drain seems to be very large for a shower.

enter image description here

Edit: I added a clearer picture with all the drains. My understanding so far is the 2" inch line is vanity drain, 4" inch line is toilet drain, 5 gal bucket is the shower drain. The 2" inch drain goes inside the wall. One thing I am unable to figure out is the vent, I don't see any vent lines in the basement, everything seems to be a drain pipe.enter image description here

  • Perhaps the centre one is for a floor waste?
    – Mr R
    May 5, 2022 at 8:37
  • 1
    A better picture without the clutter, showing spacing from the walls and diameter of the pipes would be most helpful.
    – FreeMan
    May 5, 2022 at 11:32
  • 2
    The left one looks like it might be a large hole to allow adjustment of a smaller actual drain within, which would be consistent with a shower or tub if you don't have the exact one picked out when placing the pipes. It's often the case that you'll end up breaking concrete to get the pipes where you want them anyway, unless you can work with where they are. Looking up, do you have a Vent connection?
    – Ecnerwal
    May 5, 2022 at 12:01
  • Thank you. I do not think i have a vent connection, as there are no other pipes around that area. I will get better pictures. Are my guesses correct about the other two drains.
    – Adi
    May 5, 2022 at 12:28
  • Your guesses are reasonable - it's rather hard to say from a picture and no further info if they are definitely correct, but it's not terrible odds. Looking closer, I suspect the "probable shower location" is the bottom of a 5-gallon bucket sticking up, which is consistent with my guess also being reasonable. Usual setup would be the sink location acting as the vent for the other two fixtures. You'll want to sort out a connection from here to a dry vent.
    – Ecnerwal
    May 5, 2022 at 14:16

1 Answer 1


The 2" line would be drain for the vanity sink. It'll end up in a wall and would normally be extended up to connect to a stubbed vent out the roof, sometimes left in the floor framing above.

The 3" or 4" line is for a toilet. It should be centered 12" from a finished wall. It also requires a nearby vent, but it may share the one for the vanity.

The large one likely contains another 2" line for the shower. Since shower drains require fairly precise placement they're usually boxed out to allow for some movement. Knock the box out to have a look. There's probably a cap underneath, or just a stub. Again, it will have a nearby vent.

  • I thought vanity drains were 1-1/2 inch, and kitchen sink drains 2"?
    – SteveSh
    May 5, 2022 at 22:27
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    Once a pipe goes under concrete it's typically enlarged to 2". Also, this serves as a vent for as many as three fixtures, so it would be larger.
    – isherwood
    May 6, 2022 at 13:28
  • Do I need a vent line for the basement bathroom.
    – Adi
    May 14, 2022 at 4:47
  • All drains need vents.
    – isherwood
    May 18, 2022 at 0:21

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