If I am cleaning oily or greasy parts I boil them in a large container on a propane burner. I think you can get better results with rust removal using electrolysis, sand, or bead blasting than with a sonic cleaner. I see some people have OK results using sonic cleaners for rust but it really depends on what kind of solution you are using. Where the sonic cleaners really shine is getting into small passages and crevices. I also want to try using small glass or plastic containers to put the cleaning solution in with the part and float that in just water in the sonic cleaner. That way you only contaminate the small amount of cleaning solution.