The water in a 3 foot x 3 foot pit 2 inches high is about 11 gallons.
That is how much water is running back. Instead of a small hole at the
top of the pipe, tap a hole and install a vacuum breaker, or an upside
down u-shaped pipe with a check valve at the end which will act the
same way. The pressure from the pump will push the vacuum breaker
closed, then when the pump shuts off the vacuum from the siphon will
pull it open. No water will come out where you don't want it to, and
the siphon will be stopped.

Stretch