Typically I have used a big c-clamp but on one of my old VW GTI’s you had to rotate the piston while pushing it back in so I would rent the tool from the dealer when I had to do the brakes on that car. On the VW I can’t recall if it was just the back, or front and back on that car. After owning that car I now always check to verify if I can push the piston straight back in or need to rotate it.