I use a stiff nylon bristle brush (kinda like a large toothbrush) with either brake cleaner or water and detergent (depending area) to scrub the caliper and piston area.
Can take a bit of elbow grease, but is doable.
It is important to scrub the pistons and clean around the piston seal area.
That brake dust and road grime can cause sticking pistons.
It's one of those necessary but thankless tasks to keep the bike in top shape.
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