There are fish traps that you can buy at your LFS. These are clear acrylic tubes with a bait box at one end and a guillotine style door on the other end that you thread with fishing line. You sit away from the tank with the baited trap out in the open in the tank. When the fish swims in to get his favorite food, you just release the fishing line and the guillotine door falls into place trapping the offending fish for easy removal.

They are relatively expensive, but they are worht not having to rip your tank apart to catch the nuiscance.

JimT