I use a doubled-up shipping bag to move my RTG. Dunk the shipping bag into the half-drained tank and semi-submerge with the mouth of the bag open wide. You can either try to guide the aro into the bag or what I do is use the bag to slowly capture the aro at one end of the tank.
He will not be pleased once he realizes he's been trapped so you'll want to make sure you move relatively quickly.
Try to remove a lot of the water from the double-bag before lifting out of the tank, otherwise you will have a hard time lifting it out. You can always add water to the bag once he is clear of the tank. I would place the double-bag in the container you refer to and move him that way. You will need him in the bag to land him in the new tank, so I wouldn't even bother taking him out of the bag. Seal the inner bag up and trap lots of air in it before you tie it off. Then tie off the outer bag. You'll be good to go.