I have almost threw up in my mouth before when smelling some that had been several days without opened. If you let them sit, you can throw them in the dishwasher on the top shelf. This usually cleans and takes the smell out, but the top will wear out faster this way. The tab to close where you drink out of, or the one over the hole to let air out while you drink, will fall off and I need a new one.
I think Vitamin Shoppe has them for about $2.50. I buy at least 4 at a time.