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. 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? I can only see 2 ways to do this both require a 90 degree turn since I have to run horizontally to get to the showers vent pipe (if I can do this) Working from the vanity;

Option1- use a T fitting, run one side over the sanitary tee in the showers vent pipe, and come out the other side use a 90 degrees elbow to turn it upward to connect to larger vent pipe running horizontally overhead. The other opening would be to be used to connect the vanity’s p trap into.

Option 2. use a sanitary tees and come out the bottom turn 90 degrees and run horizontally 5 ft over to another sanitary tee in the showers vent pipe. I could run out the top of the sanitary tee by the vanity to run upward to the vent pipe overhead.

Can I get some guidance or help resolving this or an I just up the creek?