Okay, either I am over-thinking this, or I actually have a legitimate question. I’m doing a basement remodel, part of which includes expanding an existing lavatory into a full bath. We’re putting a stall shower in one corner. It’s about two feet from a waste stack that serves a bathroom on the second floor. This stack is 3″ cast iron, and beneath the slab it connects to a 4″ line that in turn connects to the main sewer line. The 3″ waste stack from above is vented tthrough the roof.
I have plenty of altitude to get the desired 1/4″ per foot (or more) pitch on the shower drain. My question is, given its close proximity to the existing, well-vented stack, does the short shower drain need its own separate vent? Plan ‘A’ was to just hook the trap arm from the shower drain into the 4″ waste line, fill in the cut in the slab, and be done with it. It seems to me that connecting the shower drain line to a large, well-vented waste line at such a close distance should be fine. But then, the more I read about this, the more confused I get.
Any ideas much appreciated. Thanks!