I'm not sure if all 23.5's are exactly the same but my bilge pump is mounted in/under the port settee forward of the recessd hole for the ice chest. This appears to be a little high above the water line to do much good. Off the cuff I'd think that having the bilge pump in the lowest part of the boat would be the logical place for it. That being said, it would seem that the best location for the bilge pump would be under the aft berth. That seems to be where water collects in my boat. As an aside, if you are getting rain water in your boat check the rub rails right where they turn to rap around the stern and terminate. The rub rail housing does not fit perfectly at the turn and the old 5200 that was added to fill the void was in need of replacing. Leak problem solved.