Help with overflowing sump system

[RDNanoGuy]

You could also put a flap checkvalve right on the output of the pump. The weight of the water in the return line will shut the valve when the water stops preventing the back siphon. I know alot of people don't use them but I put them in all my systems and have yet to have one fail. Combine that with a siphon break hole up top and you should be pretty safe all round.