I have never cleaned my bike pistons/calipers You don't do it with a car so why do it with a bike??????
I usually get away with never having to rebuild them. In summer you're fine but in winter it's ESSENTIAL to wash the calipers down after every ride.I've got my hosepipe wall mounted just inside the garage door, when I get home I spray the living daylights out of all three calipers - really hammer them from all angles. Then shove the bike in the garage until next time.