CM,
The compressor washes were done with fresh water and not from a fire hose in my time. They were done on Sea Jet and plastic pig alike.
Bloke in yellow surcoat would form an intake shape with one arm and using his other hand point into it and transcribe a circle. This was usually timed perfectly to coincide with having your hands on your head whilst weapons were made safe.
Once you'd secured the air con, anti g and one other thing that I've forgotten you gave the thumbs up and some mate fired a few gallons of water down each intake.