I was concerned about them getting paint remover on the pistons too but i tried to just put the paint remover on the part that is seen on the outside. i taped off the end of the caliper so that nothing got inside. i suggest taking the calipers off the car bc i wasnt big on the idea of overspray possibly getting on my car. and i did the whole process while watchin the godfather and taking breaks to apply a new coat every 30 or so.