Will this sump/refugium design work?

[Michael]

Okay, I am setting up my 50g sump for my 72 gallon tank (corner box drilled overflow). I have a 20g tank that I want to use as a refugium.
I plan to have the water overflow to the sump, and use 2 empty canister filters as pumps to pump the water back to the tank. (am planning on purchasing another mag18 eventually.)
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--I was thinking of putting the 20g tank in the sump, and since it is lower than the sump, use it as a refugium. It will have some water movement with the water flowing over the top of it. (I could also split the overflow from the main tank and put it in the refugium, but don't think it needs that much water movement).
-Will this work?
-Will the canister filters be safe (ie not cause flooding) if their output is just at the water line of the main tank...not submerged in the tank?
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--72g, 50lbs liverock, tang, blennie, 2 cardinals, 2 peppermint shrimp, xenia, mushrooms, NO flourescent, 802 powerhead , Klaes skimmer.

Thanks

Michael