Color negative film should have something called stabilizer at the end -- it combines a biocide with a wetting agent. It used to be foramlin and photo-flo mixed together, but most are using something safer than formalin now. If your color negative process does not include the stabilizer step, you can safely conclude that that is your problem. If your school is skipping the stabilizer (which they might for safety reasons, or just because it is a pain since it cannot be done in the same tank as the processing unless you are using stainless steel reels and tanks), you could safely mix up your own photo-flo and put your films through it before you hang them up. Just make sure to take the film off the reel if you are using plastic -- photo-flo will gradually build up residue.
I also agree that photo-flo is a one time only solution -- it is so highly dilute in use and so cheap (one bottle will last you years if not decades...it does not expire) that it is not worth reusing, as the solution will pick up gunk from one film and later deposit it on another.
Finally, for dust problems, barring a forced air dryer like a Jobo Mistral, something that works really well is to have a HEPA filter in the room where you are drying. Put the HEPA filter in there and turn it on for awhile before you hang up your film, then do not have any traffic in the room. HEPAs are designed to remove almost everything that is larger than .3 microns from the air...that is really tiny. I have found good ones to be extremely effective at keeping film clean.