For a fleet, I would use paint thinner or the cheapest equivalent and a large bucket or two. Remove the offending components, and sit outside with a brush. If they're really bad, use the first bucket for primary removal of most grime, and the second bucket for a "rinse" with clean solvent. For chains, a plastic 2-3 liter soda bottle and a minute of shaking followed by a hot water rinse and a blast from an air compressor.