Okay, I am going to tell you all this trick once.Get a siphon hose long enough to reach the bottom of the overflow and into your sump.
Get the siphon going from the two,overflow to sump. Leave your pumps on so as not to run dry.This way you can keep going until the SOB is captured. Have your wife or kid hold the end going to the sump with a net that the water will flow through.While you are trying to get the fish to get sucked into the flow of the siphon, the kid will be waiting with net in hand.
I have done this at least 20 times, mostly for an Orange Spotted Blenny.
Make sense ?