I have a home build in 2003, the builder roughed in a basement bathroom with 2 drains & 2 vent pipes. I see no place to install a vanity with drain & vent pipe.
All vent pipes are connected to a drain. If the plumber gave you a good rough you should have a 4" pipe to pick up the toilet, a 2" pipe coming out of the slab to pick up a shower, (this 2" pipe could be in a 14" square hole tub dap out) and a 2" pipe in a wall to pick up the lavatory/vanity and to vent your bathroom group. This is a normal basement rough in. As a rule the tub/shower's wetvented by connecting it it to the lavatory drain.
"A neighbor said I can run 11/2” PVC horizontally (about 5 feet) and connect into the showers vent pipe use a Sanitary tee to run the vanity's drain into the showers vent pipe, is this correct? Secondly won't I need to vent the vanity’s drain? "
If f the second vent pipe isn't to pick up a kavatory then what's its function?
Your neighbor was almost correct. You may run the lavatory trap over to the shower vent and tie in with a san tee. However if the run will be up to 5 feet you will have to increase the pipe size to 2" as 1 1/2" can only run 3 1/2' by code.
If it were me, I'd tap into the shower vent with a wye and a 45 deg fitting fairly low to the ground. I believe sanitees are ok in a vertical app like that though (pro to confirm). Putting it low just makes the 'wet vent' section as short as poss."
You can not do this as you would be building a "S" trap. "S" traps are illegal in all US codes and also in Canada. Make your lavatory stub-out 18" above the floor to the center and give it 1/4" to the foot slope to the san tee.
Essentially, there will be 2 junctions off the shower vent: one for the sink drain, one for the sink vent. The sink drain line will have a split close to the drain for the sink vent.
Not quite so. There will be only one "junction" on the shower vent. The drain from the lavatory. Since the lavatory will be connecting to the showers dry vent a extra lavatory vent won't be needed.
It's gonna work like this Mike, Cut a sanitary tee into the shower vent 17" off the floor to the center of the branch. Run a 2" drain from the san tee over to a 2 X 1/2" elbo and stub out 1 1/2" to pick up the lav. It's as simple as that. Are you quite sure that the second vent isn't there to pick up t6he lavatory???
Good luck, Tom