I was always straining my back when pulling full garbage bags out of brute garbage cans. The solution that a custodian came up with is to drill a hole in the bottom of garbage can to eliminate suction when pulling the bags out. I'm sure it was located just high enough to avoid trouble if you had a leaking bag. I found this with other ideas when searching Ergonomics.

build portable steps or hook on step that hooks onto lip of dumbster so bags can be dropped in rather then lifted or thrown.