D.C. Code § 8-601: Waterclosets required.

It shall be unlawful for any person or persons to maintain, upon any original lot or any subdivisional lot, situated on any street in the District of Columbia, where there is a public sewer and watermain available for the use of such lot, any system of disposal of human excreta except by means of waterclosets connected with such sewer and watermain.