On another tack...
Have you considered mounting your return pump intake closer to the surface of the sump waterline?
When I built my 75G. tank I calculated 1 1/2" of space between my overflow and the top of the tank. That equals 5.5G.'s before it over flows. In my sump I calculated that 2" of water equaled 5.5G.'s so I set my pump intake at 2" below the sump water line.
If the overflow plugs the return pump will run dry before it floods the tank.
There is a trade off between flooding the floor and burning out the pump but the water damage from a leak on the 2nd floor outweighs the cost of the pump.
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F11