Hello,
I built my house about 3 years ago and I'd like to finish the basement. The bathroom was setup for a shower, sink and toilet. My question is how to install everything. I have 2 pipes coming up from the floor both 3.5"dia capped. I also have a square patch in the floor for the shower drain I believe (The builder said he does this so he can find it) . I assume the middle pipe is for the toilet which I don't think I need to vent. The pipe on the left is for the sink? Why 3.5 inches? Do I need to vent this? Also, I have in the ceiling a 1.5 inch pipe capped I assume for vent.. . Pic 1 Shows the Pipes in the slab from the front, pic 2 from the shower end. The final pic (3) is the ceiling where the vent is. You can see in this pic the sink drains from the bath upstairs next to the vent, and the other end is the toilet.

Thanks for in advance for any help.

Your builder's got me confused. This roughin looks all wrong to me. The commode rough in should be 12" out to center of a 3 or 4 " pipe that has a styrafoam closet wrapper around it so you can install a closet flange without having to chip the cement around the pipe. I don't see any wrapper. I have no Idea what the pipe in the middle of the floor picks up. The sink should rough out 18" above the floor and stub out from inside the wall with a vent running out of the tee to the roof or reventing back in the attic. I hope that those sharp bends near the floor plate doesn't carry the discharge from the upstairs toilet. Bad practice to use short bends in drainage. Call your plumber/builder and find out the purpose of each pipe and then get back to me and we'll sort this out. Good luck Tom