I've done similar to Alctel for many years now also with a small 500 gph pump whose only purpose is to suck out bilge water to the last 1/4" or so in the very aft one foot of the bilge -- which leaves the remaining forward 8-10ft or so completely dry all the time. The pump is fused at the DC panel. I rigged with no float. It has an on/off switch which I placed high up in the in the bilge so as never to get wet. On the discharge hose, right next to the pump, I have installed an in-line valve of the type pictured below. This pump has it's own dedicated hose to the outside -- not shared with the other pumps. When I want to completely drain the bilge, I take off the bilge cover from the cabin sole, open the valve and flip the switch to start the pump. When the pump starts sucking air, I immediately put the hose valve to the shut position. Then turn off the pump. The valve prevents water still in the hose from running back into the bilge. The valve stays closed until the next time I want to drain the bilge. The only downside to this arrangement is that I need to get on my knees and reach into the bilge.
I can't think of any other way except to do the same and instead of a manual valve, use a self closing check valve. Problem is that any 'crud" that gets sucked up through the pump can get lodged in the check-valve diaphragm which will allow the water in the hose to drain back into the bilge.
Of course for the serious bilge pump-out needs, I have two larger capacity float activated systems -- each independent of the other and each with separate hoses to the outside.
