Drain the tank down to about 6 inches (into whatever holding containers you're going to use), remove the other inhabitants, then as was stated above take an old COTTON (remember that says COTTON not polyester) Pillowcase lay it down in one end of the tank propped open with something like popsickle sticks and
gently coax him to swim in. With everything that going on most likely it would appreciate a dark hideaway. Then pick up the case and set it into your transport container.
With regards to the use of a towel, I believe it would remove alot of the fishes slime.
Alternatively, you could use a trout net. Put it down into the tank and then, again,
gently coax the fish into it.
But you really should drain the tank or you may find yourself picking that Aro up off the floor

.