Frick-n-Frags is correct, the U tube remains underwater if the power goes off. The siphon does not break. If you get air trapped in there when starting the siphon, you can insert an airline hose and suck it out.
BTW, did anyone notice the rock behind the yellow clamp. It keeps the gatorade bottle from floating up.
We have an identical tank right next to that with a regular overflow, I think the picture is in my gallery. These are being setup in my friends classroom as frag tanks.