I just installed a 10" siphon system on my pond. I placed the horizontal pipe through the dam at the maximum water level for the pond. I have been playing with the vent height relative to the horizontal pipe.

So Im a little confused. I read someones post that if I want to lower the pond I can just lower the position of the vent. I can see this to a point, but I dont seem to follow the physics once you lower the vent below the horizontal pipe. I thought it was the gravity of the water flowing on the backside that creates the suction. So if there is no water in the horizontal pipe but yet the vent is lower than the horizontal pipe, how is it possible to start a suction? If this is the case I cant see that water would flow.