If you have shop vac hose, siphon him out with it, and if that fails, Rudy suggested the only humane option that is left,
"sharpen a stick"
there is one more way, with the flow shut off, pour a half liter bottle of Tonic water, {or sprite, or 7-up},(Tonic water has less sugar-contamination) into the over flow. The CO2 will make him pass out really quickly. Fish out the limp fish and put him into a 5 gallon bucket of clean replacement water, with air if you have it! He should wake up if you did not leave him in the low O2 environment tool long. I usually hand 'swim" the fish in the clean water to force clean water over the gills. Then, siphon out the water/sprite mixture and replace with new water, put the happy swimming Houdini tang in a safe place, or give him to Rudy.