I am remodeling my basement bath that the previous homeowner installed (concrete subfloor). Their shower pan was placed on top of a small, raised platform (~4" tall) which I always thought was odd. When I took it apart it looks like the platform was to allow for the bathroom sink (green pipe) to drain into a separate floor drain (#2 in the drawing) that was under the shower pan and near the actual shower drain (#1) in the picture.

However, there is another drain going into the subfloor (drain #3 in blue) that the plumbing goes right next to. This is in the wall behind the shower and is for an upstairs sink on the level above. There is also a tie in higher up between the bathroom sink (green) and the upstairs drain (blue) that I'm assuming is for the vent.

So, is there any reason I can't eliminate & cap drain #2? Then tie in the sink drain to the upstairs drain. This would get rid of the need for the odd platform. If so where would the vent go, just straight up from a Tee (see proposed layout pic)?

Pipes are all 2" PVC except from bathroom sink to the stack. That section is 1-1/2".

Existing Layout: enter image description here

Proposed Layout: Cap drain 2, connect sink to drain #3 enter image description here

Pic from behind the wall: It is a little tight with ~6.5" (center to center) between the bathroom sink line & the upstairs drain. But if the upper connection isn't needed it would just be adding a 90 & 2x2x1.5 sanitary tee (orange). enter image description here


1 Answer 1


Ok from what I see in your diagram you can cap or plug the green shower drain underground. It should connect to the blue line underground anyway and be connectedto sewer or sump pump. In fact you can eliminate all the green drain lines except the sink. Just connect the sink drain to the blue drain line. The blue pipe going to the upstairs drain is the airline. All sinks should have ptrap.

  • Thanks for the comment. I was really confused on why they ran the plumbing like this. Especially since it required building a platform to sit the shower pan on, which complicates everything. My only possible thought was that Drain #2 was also acting as a vent for something else. But can't see the need since everything is likely connected underneath like you said.
    – Aero Engy
    Commented Apr 1 at 20:48
  • Connecting the green line to the blue may or may not be a packaging issue—if the horizontal and vertical bend radii can be done in the space available.
    – Huesmann
    Commented Apr 2 at 12:25
  • @Huesmann Not sure what you mean by packaging issue. If you mean is there enough room for the fittings. Well, it's going to be close. The 1.5" sink drain is ~6.5" from the 2" line (center to center) and it's behind a wall & hard to reach. But I think I can put in a 2x2x1.5 tee and then 90 the 1.5" into the top. It is hard to get a picture of it but I'll try to add one to the original question
    – Aero Engy
    Commented Apr 2 at 21:29
  • 1
    @AeroEngy yes: packaging = space. It's not clear if these are all in walls or not, or how thick the walls are, so...packaging. You're there, so you can see how much room there is.
    – Huesmann
    Commented Apr 3 at 11:40

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