There is a screen in the cases, but what "they" didn't tell you is that unless you split the cases, there's no way to get at it. (you can see it if you take the stator housing off, but that's it.
Otherwise, only the oil filter and two drain plugs.
These links may help you:
http://www.thumperta...9-model-yz450s/ (same as the procedure on yours)
http://www.thumperta...e/#entry4319538 (references to the '06-'09 YZ450 apply to yours)
http://www.thumperta...ter-cover-bolt/ (a neat, easy mod that makes life much nicer)
Didn't you get a service manual with the bike? You should have.