 Re: Anyone ever try this
You mean as a way to get water from your main display tank to your sump?
That won't work because in order for a siphon to be created the C tube must be submerged under water on both ends constantly. Overflows have a baffle built into them so that the C tube is always submerged in water even if power goes out. The baffle side of the overflow will retain enough water to keep the C tube submerged. I don't think you could even start a siphon in the first place, but if you did and the power went out and came back on again the siphon would definitely not restart itself and you would have a big mess on your hands.
Ebay has overflow boxes for around $40.00 invest in that and avoid the headache later.
S
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90 gallon reef, mag 1800 main return pump, 10 gallon refugium + 10 gallon sump, CPR overflows, ASM G-1 skimmer, icecap 660 vho 440 watts. 130#LR and 60#LS. Corals: Finger Leather, Fat Finger Leather, Toadstool, flower pot sps coral, hairy mushrooms. Fish: Yellow tang, Bi-color angel, pecula clowns, royal gramma, coral beauty angel, yellow tail damsel, blue damsel, Sergeant Major Damsel. Misc. hermit crabs, snails, flame scallop, Xenia | 
