Check Valve,Water Pump,Stuck

I gotta say that the check valve design looked kinda flimsy and poorly designed.  

I was in the process of de winterizing the Pod today and when I hooked up the water to the city connection and turned it on. All was going well until I turned off all the faucets and listened for leaks. I heard a hissing sound that is representative of a water leak. Me being a Master Plumber these sort of sounds get my immediate attention. The hissing sound was coming from the low point drain area and so one would only think that there was a cracked water line that must have not got all the water out of it for the de winterizing process. Further investigation revealed that the hissing sound was water flowing through the water pump and thusly filling up the fresh water tank via a stuck check valve in the water pump. I took a nylon tipped hammer and beat the water pump to no avail. Now it's time to take the water pump apart and inspect the check valve. The darn thing looked fine and it did not appear to be stuck?