As part of my refit, I installed 2 sumps with self contained pumps and float switches, one forward and one aft. The normal sources of bilge water on VC are the anchor locker with deck opening for the windlass and the fore and aft air conditioner evaporators. I applied a white epoxy resin coat throughout the anchor locker and glassed in a drain system that is plumbed to the forward sump. I also ran the forward AC evaporator drain line to that sump. The aft evaporator is plumbed to the aft sump.
The next big challenge was the enormous amount of residual water that would drain back into the bilge from the oversized bilge pump hoses after the pumps shut off. The hoses are 2" internal diameter and connected to high volume pumps and 2" thru hulls. There is enough residual water in the lines to fill the entire length of the bilge to nearly 1/2" deep. The setup is designed to slow the rise of water if a major leak occurs and works in conjunction with 2 high bilge water audible alarms.
I thought I had solved the residual back flow problem by putting in check valves. However, 3 weeks after installing and testing this new system I was shocked to see it fail on a repeat test. The huge column of residual water above the check valve put so much back pressure on the valve that even these massive pumps couldn't prime and start pumping. Centrifugal bilge pumps like these are designed to self prime against a zero pressure head. Once primed, though, they are very powerful. So the check valves were removed and the pumps now prime instantly and perform like fire hoses.
This still left me with the problem of 1/2" of residual water in the bilge after the large pumps stopped. I used a small Whale diaphragm pump on manual switch with small diameter tubing and an extremely shallow homemade strum box placed in the 4" x 8" recess in the bilge. My strum box has a small ball bearing that seats on a small o-ring forming a low resistance check valve. Since the check valve is on the suction side rather than the pressure head side and is light weight, the pump has no problem priming. The result is a bone dry bilge and the 4"x 8" recess pumps down to near zero which can be blotted completely dry with one paper towel. After achieving a dry bilge I painted it with white bilge paint and installed LED downlighting. Now it will be very easy to inspect the bilge for any leaks.