Whenever I've brought in my scrap, the guys at the yard do all the separating. They're pretty good at it. It's faster if you pre-separate it to the best of your ability, though. And you don't need to clean it.
Beware of mixed metal. I had a bunch of copper pipes, and if there's a brass fitting on one, the entire pipe goes into mixed, which pays less.
Ditto for old screens that still have the mesh in 'em, that sort of thing.