I have a basement sump pump which operates as it is suppose to. The pump operates till the water level drops and the float switch kicks the pump off. But at this point the outgoing water effectively siphons the remaining water out of the sump causing the pump to become air-locked. After becoming air-locked, once the sump has filled the pump will run continually for days without pumping any water.

I'd like to know if there is a anti-siphon valve I can put in this system to stop this from happening. Alternately I've also been thinking about drilling a hole in the discharge line above the pump but before the check valve.....Just wondering if this is allowed by code.

Any suggestions would be greatly appreciated.