What grade Walnut shell needed for interior fuel tank cleaning.

[Magic]

Hey guys and gals, The inside of fuel tanks has a light rust covering nothing harsh or flaky. The outside paint is perfect and don’t want to change that for sure. I’ve read about wrapping the tank in thick blankets taped so they don’t unravel and placing it in the clothes dryer acting as a tumbler on cool no heat of course. Making sure that the tank wrapped in blankets doesn’t move about while tumbling with my choice walnut shells. There are of course different sized shells or media grade. Would coarse shells that are said to not damage metal or a finer walnut shell grade? These tanks sat empty for 5 years in a garage. When I rub my finger inside as far as I can reach lol I get smooth rust color easily with no hard edges at all. The inside of the tanks are not completely covered in rust color about 50/50. Any experience out there or other advice outside what I mentioned to clean them up inside is appreciated. Thanks, Merlin