The vast majority of waterless urinal manufacturers design their fixtures to fit with conventional plumbing systems [source: Stumpf]. Many large fixture producers, like Kohler and Sloan, even have their own waterless toilet lines. Of course, it makes business sense to keep them adaptable since waterless urinals can be a tough enough sell as it is, for some. Specifically, waterless urinals usually fit standard 2-inch drainage lines, or can be adapted to fit 1.5-inch lines [source: Waterless]. Since they don't need any water for flushing, they don't need to be hooked up to a second line for potable water supply.
If you've ever seen a waterless urinal, you might have noticed a pipe protruding from the wall above it, with apparently no purpose. That pipe is the unused water supply line, which needs to be capped when waterless urinals are installed to replace traditional urinals. Since waste water won't be flushed out with a fast moving stream of water, the pipes leading from the urinals to your waste line need to be sloped enough that waste can drain out easily. Those pipes need to have a slope of at least a quarter of an inch per foot [source: Stumpf]. If the lines aren't sloped enough, they will have to be modified, which involves replacing the few feet or less of pipe leading from the bottom of the urinal to the main waste line [source: Falcon].