I think I've actually figured out how those trash cans work. I think they just take a long time to reset, probably a day, maybe a few days, maybe half a day. And then they just have a chance to have an item or a pokemon in them.
On another note, I'm gonna start transferring pokemon up to Black in preparation for Pokemon Bank. I have Ruby, Emerald, LeafGreen, Soulsilver, and Black on hand, and friends that have FireRed and Sapphire. If there's anything you want, let me know. I can clone any legendaries found in Gen 3 with Emerald.