Rebuilding hardware set up

[pterfloth]

The return line I mean is the return line from your sump via your return pump from the sump to your tank. Water can drain from your tank into your sump during a power outage in two ways: through the overflow until the water level in the tank drops below the top of the overflow and secondly, it can siphon via the return line from your sump return pump back into the sump. One should set your maximum sump water level so that when both the overflow and the return pump drain to the sump there is enough room to handle it. The overflow may not be the problem but return line back to your tank may be submerged too low. You can fix this my raising the return line and not submerging it so much. You should check this and adjust it in any case.

What I suggested was that shut off your return pump, immediately raise the return line out of the tank and then allow the tank to drain via the overflow until the overflow stops. If this is already enough to overfill your sump then you need to lower the level of water in your sump.

I know the scary feeling you get when the sump starts to fill. This is a solvable problem.

Hope this helps. Feel free to ask for more specific advise.