When the vent tube is uncapped or above the water, you will never attain a "siphon" as air is being pulled into the pipe from the vent and it only drains. A "siphon" starts when the vent tube goes under water AND the top pipe is below the pond water height, then, flow velocity is increased drastically due to the head water weight shifting to the drain pipe inlet rather than head water weight being only above the top of the crossover drain pipe.
Last edited by Rainman; 06/10/13 09:02 AM.
