I am intending on finishing my basement and using the existing plumbing rough-ins to put in a bathroom. I am having a little trouble making sense of the rough-in layout - see the attached drawing. I understand the stub through the floor is for the toilet and I believe the box out contains the drain line for a tub. Then I have 2 pipes in an 'h' shape which I assume are the drain line & vent for the sink. The overlapping placement of the sink & tub rough-in seems odd to me, nevertheless it is my intent to only have a toilet & sink, no tub or shower. Which part of the 'h' should I plan on tapping the sink drain into? Do I need to fill in the box out with anything if my sink vanity covers it up?

Are you planing on a installing a tub. Without being there to check it looks like the left hand raiser is the vent for the tub and the right hand one could be a raiser that you could cut a tee into and stub out for a lavatory. Both pipes appear to be vents. Of course all this goes out the window if the pipe coming down from upstairs is the drain line for something. Have a great thanksgiving day, Tom

Thanks for the response. I believe you are right, that the line going upstairs is probably the vent for the tub as I think I have accounted for the other drains in the house. It appears that I should be able to stub a sink drain into the one on the right. It just seemed an unusual rough-in layout to have the tub sandwiched between the sink and the toilet.