Acually, they don't have too, as i've read, and since had a personal story related to me about.
I forget where, however there is a website dedicated to
peeing standing up for women. http://www.restrooms.org/ It involves basically either just unzipping, and probably unbottoning your pants/shorts, holding open your
labias, and using your fingers to aim your
urethra. They also have small little plastic
thingys that one can insert over the urethra which basically gives them a larger little
penis to pee from.
The site also said that if done properly, it almost eliminates the need to wipe after peeing, as little-to-no
urine gets on you because the labias are spread or the urine exits through a
tube.