I respectfully dissagree with Dog on that one. I respect what he say, but I dissagree here. I believe a checkvalve is a good system, but requires maintenance and requirs you to carry a replace. Generally you can clean/repair these yourself. Don't give up on theis one yet. At the bery least, you might be able to use it as a spare.
THe check valve is to keep the water between the two to keep from flowing back into the bilge. It serves a good purpose. It could be argued that the check valve is a backup system... though that is not its intention.
By the way, is your siphon break centerline? Where is it on the boat?
I'll also agree that check valves are bad news. Centrifugal pumps have very little ability to overcome head pressure. 15' of 1" hose that goes to a point 6' above the level of the pump will and can often create a cavitating bilge pump that does nothing but make bubbles in the blige because it can't overcome the head pressure of the water in the hose.
Many moons ago, when I worked in boat yards, we yanked check valves all the time. A customer would come in complaining that the pump was running but the bilge would not drain and instead would just kill the battery. 30 seconds later armed with only a screw driver the check valve was gone and the bilge pump working.
If you don't like the drain back then invest the $1.39 on a turkey baster. Check valves are a safety problem and I have seen it more times than I can count. Even in brand new installations I have seen pumps cavitate against the head pressure of the static water stuck in the bilge line...
If you use a high head capacity diaphragm pump go ahead and use a check valve but if you have a centrifugal pump (Rule type) throw it away and get a turkey baster or sponge.
I personally do not like any bilge pump exiting below the static waterline as it's accepted safe practice that all seacocks should be closed when one leaves the boat unattended. closing the bilge pump seacock defeats the purpose of having a bilge pump..?
The ABYC build standard and before that, USCG advice, has been that any below waterline fitting requires a seacock that can be shut. In the most recent iteration of ABYC H-27 they loosened up the the rules around seacocks being installed to max heeled waterline. You no longer need to install a seacock above the static waterline to be ABYC compliant, though it is advised as good practice, but you always need one for below water applications..