Dana,
A clean side to an air system, means that the air goes throu all of my filters (6) and is as clean as the o2 that I use to mix nitrox. To be nitrox certified a tank must have a current hydro, vip, and be o2 cleaned, if the mixing is to be done in the tank. It is always best to use a cleaned tank for nitrox because of the fire hazard in mixing. For further information you can call me or write to my other email account.
Clay