Avoid strong ammonia and chlorine compounds. They will make the brass brittle and shorten the life of the case. Brake cleaner can't be re-used, so that's expensive unless it's free. It may be free to you, but your boss or shop is still paying for it. My boss has a name for taking supplies from the shop. It involves Johnny Law and not working there anymore. I don't know what is in brake cleaner or the solvent, like many cleaners it may be chlorine based. A tumbler is a good choice . A decent kit with sifter, media and polish is around 45 bucks. It's cheap to feed it walnut or corn cob, one bag will do ten of thousands of cases and you can let it run at night when it won't bother anyone.