No, I said the more often possible. After three days without washing your hair goes greasy, knots get harder to unknot, and stuff you don't want start to accumulate at the base of the hair, weakening them. Plus, this probably also smells and long greasy hair are really unappealing anyway.
To dry them, just put a towel on them to absorb most of the water, then wrap a dry one around your shoulders and let your hair dry naturally. Brushing them while they're still a bit wet is what you should do.
For the brushing, as >>9 said it depends on how strong/straight/bold your hair is. But the idea was to brush them as soon as you do something that might end up with lots of knots.