Injection Molding and Extrusion - Purging

Quick question for anyone that does injection molding and extrusion. Does any purchase or mix a purging compound to clean out the screws/barrels? If so, would you mind sharing any information.

I used to work at a place where we injection molded optical plastic for DVDs.  We didn't use anything to clean the barrels for purge we just heated up the barrel and then purged the hell out of it... purge being just shooting loads of plastic shot through it.  We'd purge enough so that the plastic looked how it was supposed to look when it was coming out (otherwise it would be like milky white and bubbly).  Once it was flowing good we were ready to rock.

It wasn't food but the temp of the barrel was pretty high so I guess I'm not sure if that's a perfect answer for you but it was injection molding.