The biggest culprit for rust is of coarse, water!
Our Grandfathers, never washed cast iron cookware using soap and water. I don't either and many in these parts that use castware will have a fit, if you would try to wash in soap and water!
For a seasoned cast iron skillet or pot etc., just empty-out, wipe out clean and oil lightly inside and out. If you have some "stickies" of food product that won't wipe-out. Use one of those POT WISKS scrubber, that many Traders sell and scrub the gunk out before oiling, or wad-up a sheet of aluminum foil or a handfull of dry leaves.
Now back to the main topic!..Go to the Hardware Store or Menards, Home Depot etc. and buy one or two bottles of Naval Jelly. Follow directions on the bottle and wipe clean with only a damp cloth and dry immediately...then oil when all rust is gone. As far as sand blasting. You can take the dutch oven to a Monument (tomb stone) business and they can do a great job in most case's!
That's my story and I'm sticking to it! :thumbsup:
Rick