I'm planning on installing a bathtub on a second floor addition I'm adding to my house. I have 10" joists up there. Is there going to be enough room to put a bathtub drain and trap underneath this? I can't go directly down either, and must do a 90 over to where I can connect to the main drain down. Would a P-trap be allowable here? Should I leave some kind of access point to this area?