I realize I should've asked a question, not added on to an existing question looking like an answer, whoops...
I am tapping into an existing 2" drain to add a washer, and the trap ended up pretty high in the wall to go above the existing sink connection on the other side of the wall. What's the absolute minimum drop you would use from the box to the trap? 18"? And/or secondly, how high up the wall is it reasonable to put the box (min 36", is there a max?)