I have two drains (horizontal runs) both the Lav and Tub are properly trapped and both are vented through my attic less than 2 feet from both of thier own traps that enter my basement and connect to a verticle stack. Because I plan on making a small configuration change to how the two horizontal runs (Lav and Tub) tie into the verticle waste stack I need to know if a DOUBLE WYE where those two drain meet my verticle waste stack is proper. Perhaps you may have a better suggestion as well rather than a DOUBLE WYE. See attached photo. I'll remember to keep proper slope on all horizontal runs of course. My goal is to run the drains between the floor joists to reclaim some of my basement head space. Both those drains are vented prior to the verticle waste stack so WYE I believe can be used.