Am installing basement washroom, tub toilet sink. Will be very close to the large copper stack that all the rest of the house drains into. There is a vent from the laundry tub that goes in to that stack at a higher level. Do I need to vent all 3 new units and where do I install the vents? Close to the traps?Can I tee into the existing laundry tub vent. Toilet trap appears to be built in to the toilet, so where do I vent that. The sewer line under the concrete is very close to the new stuff.
tinmanpm

Let me show you a typical, (in my area) bathroom group rough in. This configuation only uses one vent for the entire group and you may revent that back into the laundry tub vent.
4" ,(under cement and basements) 3" (on first and second floor) from the toilet to the main. The lavatory to connect to the toilet drain line and vent to the roof or revent back in the attic to a existing roof vent. The tub/shower to connect to the lavatory drain line and be wet vented by it as will the toilet. Be advised to always check local codes before changing or remodeling your drainage system. Good luck, Tom

Let me explain about wet vents.
With wet venting, fixtures that are relatively close to the soil stack (main vertical drain-waste-vent pipe) are connected directly to it, even if the section of stack above the connection serves as a drain for another fixture. For example, the new bathtub's drain might connect to the stack about two feet beneath where the lavatory's drain connects. That short section between the two connection points is a drain for the lavatory and a vent for the tub--thus it's a wet vent.
The maximum allowable horizontal distance from fixture to soil stack and the required size of a wet vent's pipes are strictly governed by local plumbing codes. Most require that a wet vent's pipe larger than normal and that all fixtures served by the wet vent be on the same floor. And now you know the rest of the story. Good luck, Tom