DONT PUSH THE PEDAL TO THE FLOOR WHEN BLEEDING!!!
Put a small block of wood under the pedal to prevent this. This will stop you from depressing the pedal to the floor, which will prevent the master cylinder rubber from going into that part of the master cylinder where it does not normally go. That part is exposed to moisture in the brake fluid and tends to be pitted vs the part the rubber rubs on, which is shiny. This will avoid causing excessive wear on the rubber and a leaky master cylinder.