Abstract: A waterless urinal meeting U.S. sanitation code requirements and providing advantages of cost savings, water conservation and easy maintenance is particularly beneficial in public or institutional urinal facilities. An odor trap cartridge unit is configured as a coaxial dual chamber bell trap that eliminates the need for conventional P or J type traps required in water-flushed urinals. In the odor trap, a body of oily liquid sealant, floating on a body of trapped residual urine, serves as an odor barrier but allows entering urine to immediately permeate downwardly through the sealant and proceed to a drain without requiring flushing. The odor trap is molded from two plastic parts that are assembled together to form a cartridge unit that fits readily into a receptacle cavity of urinal bowl configured for wall mounting. The cartridge stays in place by friction and gravity, and can be easily removed with a special tool.