Years ago when I flew helicopters off shore, (1969/70), we had to do a compressor wash after each flight with water, to get rid of any salt contamination. It was on the WS55/III Whirlwind with a single Gnome engine and a rig was used that fitted over the 'bullet', I think about once a week we did a 'wet' wash, i.e. engine running at idle and the wash was part water part kerosene, but I'm not certain about that last part.