Are you assigning Print Queues to the SYS volume? When I see our SYS volume get filled up, it's almost always caused by huge print queues.
Each time someone prints to a network printer, the request is submitted in the form of a file that gets stored in the queue for that printer. The server sees something in that printer's queue and tells the printer about it. When there's a problem (the printer isn't online, or the printer isn't being seen by the server, and so on), the printer's queue never gets emptied out. Requests keep getting stored in the print queue. That fills up the space on the volume that the print queue is on.
If that's the case, the solution is simple. Look in the queue folders for the print queues and start by deleting the files that are in the folders that take up the most space.
Of course, once you get the print queues back down to their proper size, you need to figure out what caused the queue to get so full, or it'll happen again!