Does he eat like crazy when you feed? Mine always did on the past and this is how I did it.
Using a 1 litter soda bottle cut at the top and flip inside out like all the other fish traps. Then I poke 2 holds in the top and side of the trap, one I insert a suction cup onto the inside of the tank. The other would be at the top big enough to put a eye dropper in. I use the top hole to shoot the food in, and bait the fish in. I then wait for him to go in to eat and boom, done. For a back up I usually cover the entrance with a net immediately in case the fish does find its way out or the trap opens when you pull it out.
Good luck! Let me know if that doesn't make sense.