Easy DIY Fish Trap

I have a yellow watchman goby that I nicknamed Houdini.  A few days after placing him in my tank he wasn't coming out to eat.  A few days later I was working on the skimmer in the stand and happened to look up and see him swimming in the bottom of the overflow!  I have no idea how he got in, and didn't have any ideas how to get him out.  A few days later he magically reappeared in the main display. 
Last week the little bugger was back in the overflow again.  Since the last time he was in I made a change to the overflow pipe, so the water level in the overflow was lower and he had no way back out. 
I took a 5" piece of 3/4" PVC & rubberbanded a piece of veil to one end to cover it.  I tied a string to the other end and let it sink to the bottom of the overflow.  Within 15 minutes he was in the pipe & I pulled him out.