I used this same method to catch my blue damsel.
Although i used a two liter bottle.
I put a small amount of formula two in it and about a 1/2 hour later he was out ot the tank.
I tried every method i could think of to catch this very smart bugger with no luck. Than i remembered the minnow traps we used to use as a kid down at the creek. They were basicly the same thing but made of wire mesh. Worked like a charm once again. I guess fish are fish weather they are in a creek or a tank.