If it had inert gas before why do you want to clean it?
It would be prudent because you don't know the history of those cylinders - or more importantly if they have been contaminated. As an example - I know of a compressor filter stack that was improperly installed (a tab was not removed from the filter insert) - causing condensate (oil / water) to thoroughly contaminate the entire system (lines and bank cylinders.) Oxygen service implies that a component is verifiably clean of hydrocarbons, rust / corrosion, etc. Choosing not to clean - would be imprudent.
You might check out the Oxyhacker Guide for additional details (or take a PSI OCCT class.)
As a practical matter - in the case above - the shop used a pressure washer / (and or steam) to clean the banks and bottles. Alternatively, you might consider using a six stage process:
1) Gross cleaning. (remove valve, examine interior for rust or gross contaminates)
2) Precleaning (if needed (rust) tumble with ceramic media and appropriate solvent: Blue Gold, Simply Green (I like Simple Green Crystal - no fragrance or coloring)
3) Cleaning (tumble with glass beads and NOC (Naval Oxygen Cleaner (NOC) $$$), TSP (don't use with aluminum) Consider using an O2 safe rust inhibitor
4) Rinse thoroughly and dry. Consider using really hot water and either modified Grade E air or inert gas to speed drying and prevent flash rust.
5) Verify Clean: (White Light, Black Light, PH strip nuetral (all caustic cleaners removed), Shake Test (all solvent removed),
6) Label and reassemble with appropriate technique (correct CGA valve, no hydocarbon contamination, no silicon, etc.)
Oxygen fires are no fun... Be safe and have fun!
