I have one I made quite a while back to catch a foxface that needed a new home. Its pretty much exactly as decribed in the previous post. The door has a catch that is released manually with a line. I didn't add a feeding tube, I just placed the food in manually or used a syringe to shoot it in the open door.
It worked perfectly the first time. I placed it in the tank for a few days to let the fish get used to it, and get used to the idea of it being a good place to dine. Then once it was not so wary, I was able to easily catch it.
I recently tried to catch a Domino damsel in it, but the wily b***h was the only fish in the tank that would not enter the trap.
Ever.
All the rest of the tank inhabitants would happily swim in for the treats without a worry in the world, but the one fish I wanted to catch would absolutely never go into it. I finally had to resort to a long and determined effort chasing her around and cornering her with several nets to catch her.