1: Use a loop of wire to attach one end of sling to hole in bottom of throwing arm.
2: Shape a loop of wire so that it easily slides in and out of release slot. Attach this wire to other end of sling.
3: Pull throwing arm to loaded position. Tape a loop of wire to the back of the pouch so that it protrudes through the slot in the trigger mechanism.
4: Use a straightened paper clip as the trigger pin. Attach a string to it so you can pull from a safe distance.
Proceed to loading your trebuchet.