If you have never topped off the rear brake reservoir, then you don't have to open the system. Loosen up the two brake pad pins then remove the caliper. Remove pins: pads fall out.
Use brake cleaner to clean off the pistons. As far as seating the pistons
use a screwdriver before pad removal (and after cleaning up with brake cleaner) to spread the pads apart thus pushing the pistons home. or with a pad covering the pistons, squeeze the pad to the caliper. (C-clamps are clumsy).
There are schools of thought as to why one would let loose a blast of brake fluid...
PS: Removing the brake line clamp at the swingarm affords more movement of the caliper. And that wire loom thingamjig too.
