Ahhh yes I ran a test run i have more then enough room in my sump for the overflow if power ever goes out. I see now, ill do that exaxtly. Makes perfect sense thanks brotherStop!
Post a picture of your main tank first, so that we can see your overflow.
I have been assuming the you have an overflow at the top. If you are siphoning from the bottom of the main tank, you will flood out your sump.
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No I have overflows and when i get home from work I'll get yall a picture! But no it all makes sense now. Like I said I did a test run turned my pump off and let all my water flow down too make sure I had the room which I do