Did you hear someone saying GI meaning "To clean (barracks, for example) thoroughly for or as if for an inspection"?
I am not a teacher.
Note - Am Eng only, if at all (now). The british army jargon for menial tasks usually take the form '<sort-of-thing>-bashing' for example 'square-bashing' = drill on the parade ground, 'spud-bashing' = peeling potatoes, 'crock-bashing' = Washing up... (these terms may all have died out since my eldest brother did his National Service in the late '50s). I don't remember what, if anything, he said for cleaning. A general informal word for cleaning in Br Eng is the verb 'blitz' - but this is not specifically army jargon.
'GI' is also a slang term used in the military to indicate a 'general inspection' of the barracks. "The men GI'd the barracks before the general came to inspect."