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Obviously someone has hacked CD's account here, the real CD would never advocate putting a balky, problematic, flow restricting check valve in a high capacity bilge pump line.
T34C has the real answer, if you want a dry bilge you need a pump with a small diameter discharge that immediately goes up and through a loop or hump of some kind, so there will be minimum backwash when it shuts down. If you want high capacity bilge pumping, you need a pump with a huge discharge line--which will drop more water back in the bilge. By using two pumps, you also are relying on the "sipping" pump to deal with routine drips, leaving the larger pump with nearly no wear on it, until you need it. (And obviously separate float switches for the two, at different levels.) That also means you can wire up a bilge alarm on the same switch as the larger pump, knowing there's no reason it should ever go off unless you've got a major problem.
Go small and cheap on the "sipping" pump, and if it drains though something small and close that you always leave open, like the galley sink or the cockpit drain...no big deal. Less hose, less rise, less backwash.
That's what the other pump is there for anyway.