I use a Kadee brush to clean really dirty wheels, but more for heavy crud or rust (Aristo diesel wheels are plated steel, the plating wears, the wheels rust)
For most cleaning, wet a thin cloth with a household ammonia-based cleaner and run one truck over it while the other truck picks up power, repeat for other end. My steamers have pickup from the tender also, so that works.
For unpowered wheels, a stainless wire brush in a dremel motor tool cleans them fast, and you can also detect if the wheels spin freely.
Greg