How do I clean badly stained aluminum?

scrub aluminum pans with a wadded up piece of aluminum foil.
cream of tartar and salt is a good scrub for aluminum.

I have heard that rubbing crumpled aluminum foil will remove rust. I work as a professional cleaner and I use Windex and dry rags to polish off water spots. Hope this helps.

if it is a pot, use apple peels ( 2 OR 3 apples) into some boiling water in said pot and simmer for about 30 mins. if it is not a pot, do the same and simmer whatever it is in the water for same amount of time cream of tarter also works (-: