Here is what I have done, and it works fine. I have an outboard, and as said earlier, both the Whale and the Rule 3600 ghp pump. As for the electric pump, my figuring was that if I was going to the bother to install one, for the added few bucks, why not put in the largest.
The pump and float switch are in the lowest part of the bilge, approximately alongside the sink counter (but obviously far below below), with the switch facing forward. The 1 1/2" flexible hose (as I recall - it is standard full sized for that pump - no reduction) runs under the floor board going aft, coming up next to the rudder stem, running to the top of the stern lazarette bulkhead on the starboard side, through the bulknead, down the aftside of the bulkhead under the stern lazarette floor and out a through hull fitting. The fitting is a lexan/marelon whatever fitting mounted through the hull bottom just forward of the transom. It is normally a bit above water, but can not be seen (unless you are in the water looking up). The discharge shoots down, rather than out the back which it would do if mounted through the stern.
The pump is fused with a 20 amp fuse (not the 25 recommended - because my electrical panel isn't rated for 25 amps. I have not had any trouble with the fuse failing. Make sure all electrical connectors in the bilge are the waterproof kind.
Anti siphon protection is mandatory. Do not use a check valve. For anti-siphon protection, I have done is to put a 1/8" hole in the top of the discharge tube in the stern lazaterrt at its highest point where the hose runs through the bulkhead into the stern lazarette (it is for the anti-siphon protection that I made the loop to the top of the lazarette bulkhead). When the pump runs, yes some water does come out through the little hole into the lazarette, but that area gets wet anyway. If you want to control the direction of the trickle that comes out, put a 1/8" hose in the hole and direct the water to the side (but do not drop the level of the drain hose or you will lose the anti-siphon capability.
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