Tip for cleaning brake calipers (including the pistons).
Get a big bottle of Pine-Sol, the original variety (not the fancy smelling ones). Cut the top off a suitable plastic jug (I used an old laundry-detergent jug), one that is just big enough to contain your entire brake caliper. Support the plastic jug beside your bike in a way that you can hang the entire brake caliper (brake hose still connected but brake pads removed) in the plastic jug and then fill it with Pine-Sol so that the entire brake caliper is immersed. Leave it sit for half an hour.
Now go after the brake caliper pistons with a toothbrush and/or spray them with brake cleaner (the built-up mung will come off very easily), then push the brake caliper pistons back in, then clean the entire brake calipers with soap and water and dry them off, and install your new brake pads. You can re-use the Pine-Sol for the other side ... I keep it for subsequent cleaning jobs.
The Pine-Sol softens the deposits on the brake calipers so that even in the parts of the piston that you can't get at with a toothbrush, the seals in the brake calipers will just push the deposits loose, and then when you clean the calipers with soap and water, the loosened black stuff will come off easily and your brake calipers will look like new. It won't damage the seals.
Nice idea !
I usually add a drop of brake fluid under rubber boots , after the cleaning , to lube the pistons and seal as they are pushed back in . I don't think brake cleaner is a great lube ..