altered their drawing - does this help?
Red area can be closed by ball or screw or neither.
Not really as I am thick. If I start to undo the screw I would be venting air or water out of the system but is that not the same screw that I would undo to dose the system, which then work in the opposite direction?
Also as already asked do you professionals vent the magnaclean after you have cleaned it out?