Siphon tubes are basically a static device with a fixed
transfer capacity. Once the liquid head or liquid level at the
inlet of the siphon tube drops too far the siphon action will
break and upon a resumption of the water level it will not draw
water until the tube is primed by exhausting the air in the tube.
This priming, in irrigation practice, has been done manually
by first filling or partially filling the tube with water and then
placing it in position across the ditch bank with its inlet in the
ditch water.