One has to be lower in elevation. Agridrain level controls work the same way - again, however, you need a change in elevation. If that's not possible, you can dig a pit below the gate valve tube [like I have done] and collect fish in a horse tank. Somewhere on the forum I provided a video and photos of this. Works like a charm - few fish get caught on the pond side, but they are easy to walk and collect in buckets following draining.

Many men go fishing all of their lives without knowing that it is not fish they are after. ~ Henry David Thoreau

[Linked Image from i1261.photobucket.com]