Should the pump fail there will be next to nothing going back into the sump. Likely, no more than a half a liter, give or take...How much water will the fuge put in to sump on a pump fail?
Neat fix by the way, you obviously planned it that way!
It was planned that way, but only because when I had the tank running years ago I had my valve stuck and could not close it. Light bulb moment and a trip to the hardware store and that moment of fret was licked.