Having learned in Miesville (MN) that "other uses" of a roller towel may be dangerous, it was interesting to learn a couple of weeks (that's a fortnight for non-American readers!) ago in a bathroom in Libertyville (IL) that you should:
Wash your hands for 20 seconds. That's the time it takes to sing happy birthday twice.
My thanks to the Lake County (IL) Health Department for working that out.