I find that if I go more than about 1/2 a season without cleaning them, they start to fill up with goobers. Not that this grosses me out, but they stop sounding right.
I soak mine in hydrogen peroxide. You don't get that lovely cinnamon flavor, but they're reasonably sanitary. Afterward I rinse them in tap water. And if it's been a while, I'll blow through the "wrong" end just to blow out any goobers that may be lurking.
I once found half a Wendy's single with cheese in one that way.
