You need to cap both ends, fill the pipe, cap the tee, uncap the pond end underwater, and almost simultaneously uncap the lower end. I recently siphoned down a pond, and it wasn't easy getting it started. Any air in the pipe can break the siphon, or slow it down. If you have even a little air in the pipe, and uncap an end, the bubble will try to run up the pipe, and could break the siphon. Been there, done that.
The best way to start a siphon, is to get a trash pump, and fill the pipe with pressure from the lower end, with both ends open and no tee, with the pond end in the water. Once the trash pump forces all the air out of the pipe, you disconnect from the pump, and the siphon will flow, guaranteed. You will need a source of water at the lower end. A 100 gallon tank should suffice.
The way you are doing it now, air remains in the pipe from the pond level to the tee on the pond side, a considerable distance, so any siphon will not sustain itself.
Last edited by John Fitzgerald; 08/22/22 09:58 PM.
