One of those little ones you often pick up in fuel stations? I have one of those, but have never thought about using it for caliper pistons? Sounds good though. I'll give it a go! Cheers!
I have one of the above that i've had for over 20 years and used that on my previous 2ma and current 1kt calipers pistons and spare front caliper pistons with good effect using adaptors supplied with it.
A bit of plusgas beforehand also helps loosen them,and they can blow out with considerable force when they eventually loosen up,spraying the trapped remaining fluid inside everywhere,so be careful and wear eye protection and latex gloves.