Can an elbow be used with the heel inlet in the vertical position for connecting 2 drain lines such as a separate shower and tub. I have seen posts that say this is not the intended use for this fitting, however it works, and that better practice would be to use a sanitary T with side inlet? The vent would be coming off the tub line a few feet away from the fitting. Everything connects to a vertical drain going to the floor below. I am trying to avoid drilling more holes in floor joists that are already drilled to death! Thank you.