At this point, with the front cover removed, the final component is the rear portion of the pump. This contains the pump piston, which is round and visible on the opposite side of the handle.

Remove the two #0 screws holding the rear cover on over the back of the pump; it's between the rear of the pump and the handle.

Use your fore-finger to push in on the piston; the spring inside is fairly strong, get a helpful second set of hands if necessary.

The piston must be pushed far enough back to expose the shaft past the handle. Once the shaft is fully exposed, the retaining pin will slip out (not pictured). The pin goes in to the whole pictured.

With the shaft retaining pin removed, the piston will now push out of the rear body of the pump due to the spring tension.