If your taking the line off, brake parts cleaner, if your leaving it on just air, but never through a valve as you'll blow out the diaphragm.
So basically, you don't really ever do anything to them, but if you want to disassemble it and clean it, go ahead.
I would use anything on the valve, and water is the issue with the valves malfunctioning not oil, so a little oil in there won't hurt anything.