GoBMitch's solution will only work for pressurized water systems, which, while standard in the US, are not standard elsewhere, and it sounds like you have an unpressurized system where the water pressure is created by gravity.
If this is the case, go with ratchet freak's solution. The only problem is getting all of the air out of the pipes. The only ways that I can come up with to do this is to buy a regular ol' pump (if there is an existing drain valve) or buy a self-priming pump (more expensive.)
- If you're connecting to a drain valve (like in the first diagram,) then open the drain valve.
- Turn the pump on.
- WaitImmediately open the ball valve. (Recommended delay between steps 2 and 3: 3 seconds.)
- Wait 2-3 minutes.
- Close the ball valve (B).
- Immediately turn off the pump. (Recommended delay between steps 5 and 6: 3 seconds.)
- If you're connecting to a drain valve, then close the drain valve.
The chart shows a basic characteristic of pumping: that flow rate goes down as head goes up. Find your head requirement on the left axis and trace a line horizontally to the right. Where it hits the curve is the flow rate that the pump will put out at that amount of head. I'd aim to overshoot your flow rate requirement by 10-20%.
If I had to guess, you should only need to run the pump for 2-3 minutes once a month or so to maintain the siphon. The only way for air to get into the pipes that are part of the siphon system is the tanks are allowed to get very low or (a much more gradual process) of air bubbles entrained in the water pumped from the well get into the pipes or air otherwise falls out of solution.