I use a high presure washer/steem cleaner (has to be hot water). Then after you get the bulk of the grime off used steel wool and a good degreaser to scrub it down (being careful to not clean away any inspection markings you find)> then I use a good rust disolver like Evaporust, I soak it in a pan of it few inches deep, let it soak overnight, then roll it over to the next area, slow and possibly messy, but it works great! Once down to bare cast iron treat it with RPM bare metal protectant from ECS.