My Method.
I put the nuts/bolts in an plastic coffee container(Folgers) that I get from work filled with stoddard solvent. Paint thinner would work just as well. After soaking, I pour thru a strainer and rinse off with hot water. I then put in a different plastic pot filled with a 10% solution of phosphoric acid. Let soak for a few hours or a day, then pour off again and let dry in the strainer. I then dunk them in a different coffee container filled with some stuff I got from zero-rust called prep step which will keep them from rusting and strain again.