I've been grabbing them from work when available, e leakers gets set out and they have to pay to dispose of them. Often have oil in them, normally less than a couple gallons, which I collect and dispose of properly. I cut the top off and put it back on, including the removable top ribs, and tack the sides with a few self drilling screws. Sawzall takes out a section of tubing to make side access, and forks on the tractor make them easy to move. I had about a dozen filled with firewood last fall, down to 3 now... we keep the house warm!
But the OP was what to do with the removed bladder...
I've done several things... the bottm that's missing the top I used for a firewood tote had collected junk barbed wire when we tore out old fence, cut the bottom off and the flat side panels were cut into 6' long strips and 2 used to make a hot tub cover winter roof, some were used as siding on a chicken coop wall, some used to cover truck parts (axles, transmissions, motors, etc) that were on pallets, covered with upside down bladder to make a roof... I'm gonna cut one up to make a cover for my cement mixer next.