I am in the middle of adding a shower to my basement bathroom. In order to make things fit I want to extend existing plumbing for toilet and vanity by about 5ft. I have cut the concrete floor and found all my plumbing, including my vent stack for the basement fixtures. My problem is, I can't see where everything connects without tearing up most of my floor. It looks like everything angles towards the main drain and must all connect somewhere under the floor. I have included a sketch showing rough layout.
My question is, is it ok to add this distance to existing lines without changing the venting location?
The existing vanity has a sub-floor p-trap that I would use for the shower. As I understand there are restriction for venting distance from traps that I assume are met now, so I don't want to change that. I think I can live with the 5ft of pipe before the ptrap and whatever smells may come from there (it will just make me clean my shower more frequently).