Hello. I am just in beginning stages of finishing basement bathroom. It has been rough plumbed for toilet, sink and shower. I also have a holding tank that will have to be pumped up to house sewage line. We have a septic.

My question is about venting. There is a 2" pipe coming out of ground for sink and a 2" pipe coming up out of 12"x12" opening in foundation floor for tub. Also 4" pipe sticking up for toilet. I can see that the sink pipe feeds into the tube drain right after the trap. I cannot see where these link up with toilet drain. The all run about 15' to holding tank that has 4" pipe going into it.

Do I have a wet vent here? I have an open vent pipe above holding tank. I have already bought pump for tank... is this the only vent I need. Or do I need to also run something from the sink drain (as a wet vent). This is very confusing.

Also, I am about to start framing the bathroom and to give 15" clearance between middle of toilet drain and wall towards tub I would have to move tub drain over farther into 12" clearance between middle of toilet drain and wall towards tub I would have to move tub drain over farther into 12" hole and actually build wall with framing covering part of the hole. Seems like they could have left more room (there is plenty).

Hope this all makes sense. I appreciate any input.

They probably didn't anticipate you putting a wall in. The code clearance between center of toilet and side wall is 15", to tub is 13". If you need a wall, you can save 3" by using a 2x2 as a bottom and top plate and turn the 2x4 sideways. Once the return wall is up you can never tell the wall is only 2.5" thick. We use this technique to get "free " space in back to back closets. No, that is not a wet vent. The vent is in the lid of the sump and must be dedicated solely to that sump.

You say, "and a 2" pipe coming up out of 12"x12" opening in foundation floor for tub".

You also say, "I can see that the sink pipe feeds into the tube drain right after the trap."

Please clarify this information as it does not allow us to answer your question on venting the plumbing fixtures (sump pump vent, however, is a dedicated vent as mentioned by MA0641).

Also, look around for a FUTURE VENT (FV). Here, most homes built since 1980 or so have a FV stubbed into the basement so you can connect your bathroom plumbing vent into the plumbing system without having to tear open walls upstairs. If you are super lucky, you may find a FV and a capped off sump pump vent next to each other... would be a major money/time saver if you did. In most cases, a FV is marked on the pipe/fitting as FV, or sometimes the FV is just a capped off vent pipe (look up inside joist bays).

Please clarify the info. Requested, OK?

Mark