Custodians are people too. Don't be afraid to talk to them when they empty your waste basket. Be careful with what you throw away though... sometimes if you don't have much trash they will just grab it out of the can without taking the entire trash bag. This makes trash collection a very personal thing. "Oh no, that's not my empty Preparation H tube..."
Take care to wrap bloody knives in plastic grocery bags, shred sexually explicit love notes, and recycle empty beer cans in the staff lounge.