A device is to supply printing material to a printing material container in a printing apparatus. The device includes a first container to contain printing material, a first piston movable in the first container to exert first pressure to discharge the printing material contained in the first container from the first container, a second container having an opening to the first container, and a second piston movable in the second container to exert second pressure higher than the first pressure to form a pressure gradient based on the first pressure and the second pressure through the opening. The pressure gradient is to disperse the printing material in the first container.