Stand behind the tank/BC, put your hands through the arm pocket and grab the tank. Lift it up over your head and drop it on your back. If you don’t have an elevated place to set your gear on, dropping it over your head is the easiest way. Maybe that technique is a bit outdated for younger divers who have no idea what I am talking about. I still do this with my 130 with backplate and I am getting up there in the age bracket.