Or have it pumped out of the sump based on a float controlling the pump, then your relying 100% on float/level controllers but we use them in designing big water plants all the time with no issues as long as their maintained.Just add a solinoid valve based on float switch etc let it fill to a certain point and have the main line coming in close when the float is hit. Even if it's a backup to engineering it as a surge tank it would give me more peace of mind.