Although it may sound rather disgusting, the waterless urinal is a very effective and sanitary restroom fixture.
Waterless urinals are usually made of plastic. They do not require a water supply for flushing. The surface of the plastic is extra-slick, so liquids roll right off and into the drain.
Unlike conventional urinals, there is no chance for an unflushed fixture to sit around holding unpleasant-smelling waste. The urinal puck is no longer needed! Waterless urinals also tend not to feature rolled-back rims that are difficult to clean (unlike a toilet rim, where all that lovely black fur grows...)
When urine runs down into the drain on a waterless urinal, it is separated from the atmosphere by a special blue liquid that floats on top. There is special cylindrical trap in the base to retain the blue liquid and allow urine to drain, while preventing sewer gas from escaping. It works something like this:
_____ _ _ _ ______
| | Blue | |
| | Stuff | |_______
| |~~~~~~~~| Drain ->
| | Liquid | _______
|____|_____________|
I was initially rather skeptical about how well a waterless urinal would work, until a few were installed at Miami-Dade Community College. With fairly constant use, there is no noticeable odor around them, and the bathroom overall smells much better. They also seem to be MUCH better about avoiding splashing - I guess the shape is a lot less parabolic. See Urinals and Splatter: Whats the deal? for a discussion on the physics of that. The lowered splashing also allows the user to safely stand closer to the urinal, reducing the amount of piss goop on the floor.