Different people do it different ways - I take the plug all the way out, leave it out and usually leave in in the bottom of the water heater (So I don't have to remember what I did with it ;-)).
Others put it back in once the tank is completely drained to keep bugs and other creepy crawly things from getting in the tank.
Some may only put it in hand tight - so even if you see it there, check it.
Buddy Ray - Atlanta
Jayco Eagle HT 26.5RLS
Ford F150 Lariat, 3.5L V6 Ecoboost
Max Tow Pkg, 36gal tank
Reese Sidewinder and Reese Titan 16k hitch