Jez,
It's been a few years (like 17!) since I had to bleed Prostop and I don't have mine to reference now (maybe I can get a pic from Aaron) but this is what I remember...
The Prostop is a mechanically actuated hydraulic cylinder with one master and one slave side. On the caliper, there should be two threaded ports, one towards the top and one near the side/bottom. Get yourself two syringes (20cc) and a bit of aquarium tubing.
Attach about 4 inches of tubing to the nipple of each syringe and fill one syringe full of your favorite oil (mineral works great, does not break down seals like petroleum based) and the second about half full making sure to express the oil til there is no air in the tubing downstream.
Screw in the mechanical cylinder adjuster about half way...this sets up the master cylinder to be backed off at the end of the process as the bleading / pressurizing will set the pads tight.
Take out the ports, drain the old oil.
Push the tubing into each hole, with the fuller syringe on top.
Compress the upper syringe, filling the cylinder until pressure begins to fill the lower syringe. Slowly work the syringes back and forth, allowing any air bubbles to travel into the upper syringe.
Once your are sure all the bubbles are out and the cylinder is full of oil, gently compress the upper syringe as you retract the tubing so that the oil tops off the hole, replace the port stop.
Flip the fork over and repeat the process for the lower port, removing and replacing the stop.
Unscrew the mechanical piston adjustment so that the wheel travels freely.
Good luck!
rody