If the power is out for an extended amount of time, the main will drain into the sump until the siphon is broken because the water level is too low.
Not true with a well designed overflow, Trip. What you describe would happen if the overflow was just a simple "U" shaped siphon...but most are not.
A well designed overflow has 2 chambers, one on each side of the siphon tube. These chambers never empty, regardless of what happens to the tank level. As long as these chambers and the siphon remain full of water, the siphon will restart as soon as water starts to flow again.
40 Gal Hex, 10 Gal Sump, CPR overflow with Mag 7 return, Maxxima 35 RO
, 10K MH
pendant, 2 x 15W actinic, 1 yellow tail damsel, 1 high fin goby, 40lbs LR
.com rock, 1 red head goby, 1 algae blenny, Leather, blastomussa, sun, and hammer corals, green polyps, carpet anemone, 2 sexy shrimp...and more LR
critters than you could imagine in your worst nightmares.... Mantis in 5 gal