Alternatively, you may discharge CO2 tanks outdoors, unscrew and remove the head, and recycle with scrap metal.
Red Tank Containing Dry Chemical
If you have a RED tank containing dry chemical (sodium bicarbonate or monoammonium phosphate), put on goggles and dust mask. Discharge contents outdoors, away from people, pets, and grass, aiming low, sweeping from side to side. Unscrew and remove the head and recycle with scrap metal.