Squirrels will urinate pretty much anywhere, be it the roof of your house, or in the grass in the middle of a field. Squirrels will mostly urinate on grass when no one is around.
All mammals have similar plumbing; squirrels pee in much the same way that we do, but with smaller organs.
Yes. Yes, they sure do. They actually pee coffee from their pee holes.
Soak a cotton ball with warm water and rub it over the genitals like the mother's tongue would in nature until the baby pees.