D.C. Code § 8-204
In case the owner or owners of any such lot be a nonresident or nonresidents of the District of Columbia, or cannot be found therein, then, and in that case, the Mayor of the District of Columbia shall give notice, by publication twice a week for 2 weeks in some daily newspaper published in the City of Washington to such owner, directing the connection of such lot with such public sewer or with such public sewer and water main, as the case may be; provided, however, that if the residence or place of abode of the said nonresident lot owner be known or can be ascertained on reasonable inquiry, then, and in that case, a copy of the aforesaid notice shall be mailed to said nonresident, addressed to him in his proper name at his said place of residence or abode, with legal postage prepaid; and in case such owner or owners shall fail or neglect to comply with the notice aforesaid within 30 days it shall be the duty of said Mayor to cause such connection to be made, the expense to be paid out of the emergency fund; such expense, with necessary expense of advertisement, shall be assessed as a tax against such lot, which tax shall be carried on the regular tax roll of the District of Columbia, and shall be collected in the manner provided for the collection of other taxes.
D.C. Code § 8-204