Working on a project in Santa Monica, trying to detail the drain for a concrete hot tub set below the ground level floor, basically on grade. Do we need a P trap and/or access below? If so, do we need to excavate 18 inches below, or is there a way to access from the side? If not, can we run run it to the main drain by gravity or is it too low? We plan to use ABS piping. And the tub is deeeper than 18 in. so technically, the CBC calls it a pool. Any advice or links appreciated. thanks