I am planning a remodel and will be replacing an existing sink with a double sink vanity and also adding a new bathtub (existing shower to be removed). I do not want to cut the slab for any new drains. My question is, can I tie in the additional sink and the new bathtub drains into the existing sink drain (1-1/4") by routing them in the wall? The new bathtub drain is 8' from the existing sink drain and can sit higher to accommodate a P trap as it is a drop in model and will be set into a custom height platform. The inlet pipe for the existing sink drain enters the wall at 17-3/4" above the slab.