I use two PMUPs with three float switches. Twice a day, I pump 4 gallons out of the return section to a low point designated by a float switch (Sump_Low). Once that triggers, the water stops pumping out of the sump and I begin refilling sump with fresh water until a designated float switch is tripped (Sump_Normal). Should this ever fail, I have a third float switch (Sump_High) which acts as redundancy.
When you pump the old water out, how do you stop the water from draining entirely when you shut off the pump and gravity and siphon still exist?