I'm just starting to finish my basement, and I have a few plumbing questions and issues I want to address.
1) My configuration is this:
- My basement sits about 6' below grade.
- I have a toilet rough in that is a 3" PVC line that is currently capped about 12" above my slab.
- I have two 3" PVC risers within a few feet of eachother. One is definitely a waste line. It has a cleanout about 6" above the slab. What is odd to me is this one line appears to pick up the waste from the entire house (2 full baths on the 2nd level, a Powder Room, and the Kitchen on the main level). I verified this by running hot water down each drain, and only the one riser was warm to the touch. I'm assuming the other 3" line is a vent, but I'm not sure what it would be venting other than maybe the toilet rough in for the basement. There appears to be a shower drain (2" line capped), and then there is a separate line 2", which I'm again assuming is a vent, probably for the shower.
2) I want to raise and make some adjustments to the existing Powder Room toilet waste line. It currently sits too low. It comes down about 12" from the flange, 90's over to a T where it picks up the 2" waste line from the Powder Room sink and they run to the 3" waste riser. I have room between the joists to get it up a few inches higher, and maintain the necessary fall, so that is my plan. But, rather than tie back into a T with the sink waste line, I want to run the toilet waste right to the riser. I want to run the sink waste line right to the waste riser as well. This will not only help me maximize my ceiling heights, but it will also help minimize the depth of my bulkhead. Since I'm simply rerouting existing lines, I'm assuming there are no issues other than making sure my toilet waste line ties in below my sink waste line.
3) I want to rough in for the new sink in the basement. I have a clear shot to the 3" riser again, and I plan on tying my waste line in there. My question is do I need to vent? If so, do I vent back to the waste riser, or do I vent to the other line 3", which again should be a vent?