Don't use anything that has ammonia in it to clean brass as it will make it brittle. If you want a liquid to clean it with try Iosso, it's great for cleaning up old tarnished brass fast.
Other then that you can use any of the polishes from Dillon, Lyman, Berry's... in your media when tumbling them. Alot of people also use Nu-Finish car wax in their media also as a cheap alternate.
