I've tried a few things to prevent my sump pump output from syphoning back into the pit after each run. I went from the cheap plastic 'flap' check valves to a brass spring check valve, but still I have lots of water coming back into the sump pit when the pump shuts off. This pit is sealed and has a constant vacuum thanks to the attached radon pump.
Is there a solution to this? I've seen it suggested to put a 1/16" to 1/8" hole in the outlet pipe from the pump before the check valve, this I thought to prevent other kinds of syphon problems. I estimate that I return about half the water via syphon that was pumped out from the pit each time. I see the 9.5' head in the 2" sump pipes, and the 1-1.5 inches of vacuum on the radon pipe, and I wonder if this is a reasonably solved problem. Thoughts?