If you set the vent tube a couple inches ABOVE the apex of the siphon pipe, the pipe will act like any normal drain pipe UNTIL the pond rises a couple inches higher and blocks the air entering the siphon pipe. Gravity will make the pipe drain slightly faster once the pond is above the top of the apex, but until air is blocked, it will not siphon.
I like setting the vent a little above the Apex.
Rainman,
Question 1With the top of the vent tube a couple inches above the apex, water will drain from the bottom of the pond when water in the tube reaches the downstream side of the apex. I assume that this type of drainage is not that significant. Is that correct?
Question 2Most diagrams that I've reviewed have an adjustable vent tube. Can the vent tube be fixed with the top a couple inches above the apex? Also, can some type of "vent hose" be attached to the fixed vent tube if you needed to lower the water level?
