how does an Overflow box work?

[aquaknight]

Yea, the siphon tube is used to start the siphon on the overflow. You slide the siphon tube a bit more then halfway up the u-tube, then with both edges of the u-tube submerged in water in either box, you quickly suck out the air and water shoul began flowing.
No, it doesn't let the siphon to break, the pressure is negative on the siphon tube. The only way to break the siphon is by lifting one end of the u-tube out of the water. You can leave the siphon tube in there, but I don't, it just slightly restricts the flow.

 

[1990jpyj]

ok so i went to my LFS and they explained how it works. they said that i just put the tube in the water, let it fill-up then cap off the two ends and let it work like my vac hose works.
thanks for the help