A waterless-urinals agreement is in the can, and that means that the Comcast Center will be able to install the environmentally friendly basins in its new headquarters, a spokesman for Mayor Street announced last night. Street brokered the complex deal between the developer, Liberty Property Trust, and Plumbers Union Local 690, with support from State Sen. Vincent J. Fumo after the potty standoff was made public in The Inquirer and became a cause celebre for the city's environmental groups. The agreement clears the way for Liberty to install 116 no-flush urinals in the men's rooms at the 58-story Comcast Center,...