With bad weather approaching this season I have decided that I really need to back up my tank. The way it was rigged, if power went out water would flow over until my floor held bout 10-15 gallons of saltwater on the second story. I fixed this....I thought, but I still have a problem. The returns will cut syphon before the sump fills up and leaves about a 1" margin of error on the water level in the sump. Slowly, however, the overflow box leaks back into the sump because it is apparently not water tight. What do I do?