Here is the one I build in 2004. It was a simple structure that had two narrow PVC pipes taped to an upside down planter tray and the lip of the table so the pipes are on an incline. A tub is positioned at the end of the table to catch the worms dropping out of the pipes.
Here is the second one I built in 2007. The pipes were threaded through a crate that is taped to two planter trays set inside the table. This set up was very simple, too, but more stable.
In 2011, I used a crate again; there were two modifications, though. I replaced one of the narrow pipes with a wider plastic chute and I threaded a V-shaped piece of plastic through the crate so it directed the worms back into the table itself instead out of table into the tub next to the table.
This year I created three versions over two days before I was satisfied. The first one used a crate, the narrow PVC pipe, and the wide chute. Two clear tubes were also added.
I had a clear plastic flexible tubing that I wanted to wind around the crate, but the diameter was too big to fit in the holes of the red crate. There was also a problem with securing the clear plastic tubes. I used a plastic container so the incline would not be so steep, but the plastic container proved to be unstable even with lots of tape. In addition, I could not thread the narrow pipe through the crate to give added stability to the structure.
For the second version, I used a green crate that had round holes big enough to accommodate the flexible plastic tubing I wanted to add. Before I even inserted this clear plastic tubing, though, I ran into problems securing the tubes to the crate. I really wanted to thread the narrow PVC pipe through the crate for stability, but could not.