my friendly local motorbike engineer has modded a pipe with a schrader valve and he connects to his airline ,
he helped me a couple of years ago,we wrapped the caliper in cloth,and used gloves ,the piston was stuck,and with penetrating oil
we got it to move a little,pushing it back in until it moved enough to come out,
just popped into my hand with no real force,
needless to say ,a good clean and new seal did wonders,