Are you dealing mostly with rust, or grease-based sludge? Trisodium Phosphate (concrete cleaner) with HOT water dissolves greasy deposits. Phosphoric Acid is the classic rust dissolver, but it can be hard to find. Muriatic acid (used for cleanup of masonry jobs, bricks, etc. is very aggressive, but it works quicker than phosphoric. Most anything that we used to use back in the dark ages to clean up engines before rebuilding has been outlawed by the tree huggers- - - - -like an Oakite solution in a boiling tank, for instance. They claim if you use that stuff, all your kids will be born naked! I've built a wood fire around a 55 gallon drum of water, with a heavy dose of laundry detergent and sodium hydroxide (lye) in it, followed by a boiling water rinse and/or a pressure washer.
Jerry
