Get 2 strings, some small rocks, rubber band and some fish food (for your tang I would get seaweed.
Tie one of the strings (long enough) to one end of the cage:
Tie other string on door (botton half) with a rubber band so you can add a Frag Peg to it for weight
Put some rocks in the side of the trap so it can dangle in the right direction
Put some seaweed in it with a clip
Dangle the trap in the tank and pull the other string to open the door.
Wait until tang goes in and release the trap string... Feast on the tang
I actually tried that when I was trying to catch my flame angel. He couldn't go in the the trap. The pet keeper that I purchased is too small for my tang so I can't try it this time. I ended up getting a trap from Jeremy. Thanks though!