I've replaced a sump pump in my basement with one of the same make and model. However...the pump will not shut down when the water level drops. It has a diaphragm switch, and the troubleshooting material said (if the discharge pipe included a check valve, which it does) to drill a 3/16 hole in the pipe about two inches above the discharge connection. It still will not shut down. Anybody have an idea what I may be doing incorrectly?