Around 40 odd years ago now, as an Apprentice at the time, often used to have to work inside the fuel tanks on Aircraft undergoing major checks and overhaul, we had to wear special clothing and footwear so as to not leave anything behind in the tanks.
You would not believe some of the things we found in tanks, including on one Lockheed L188 Electra one day, not 1 but 2 heels from someone's shoes.
This is as well as the filings you are talking about, and rivet heads etc etc............