Here is a picture of how you can build a siphon that fits into the top of your standpipe. Since yours would be 25' in the air it might be to risky to install but at least this gives you some options. Here is a basic parts list.
Check valve
Ball valve
pipe
2- elbows
t- fitting
plug
The check valve goes inside the standpipe and the ball valve goes on the back side. The length of pipe inside the standpipe will determine how far down the water will drop. To get it primed you will close the ball valve and fill the pipe with water through the top of the T fitting. When it is full you will cap the T fitting and then open the ball valve.
