I made this system last year, with terrific results. The fish were the least reliable part of the system... a few jumped out! I solved that with wire mesh over the buckets.
The system is simple, and can be set up in about an hour once you've collected materials. There are no fancy fittings or valves. Essentially, it's all just cutting hose and drilling holes!
Here is a video.
The thing that throws everyone is how the system drains... it does so simply by shutting off the pump. A "reverse siphon" forms in the lines that deliver the water... so the water simply returns into the sump below via the same tube.