use a contractor grade bag....get them at most hardware stores...also like the cooler idea, but i guess that depends on what options you have for coolers, i have a bunch of different sizes from fish purchases. towel idea would work, more like moving a whale or dolphin, but the principle is the same. in short, the constant answer is to get most of the water out of the tank to limit mobility of the fish, and then don't use anything that might cut or tangle the fish.