D.C. Code § 34-2103
The Secretary of the Treasury, notwithstanding the provisions of the District of Columbia Appropriation Act, approved June 29, 1922 (42 Stat. 668), is authorized and directed to advance, on the requisition of the Mayor of the District of Columbia, made in the manner now prescribed by law, out of any money in the Treasury of the United States not otherwise appropriated, such sums as may be necessary, from time to time, to meet the expenses of the District in connection with the construction, operation, maintenance, expansion, relocation, replacement, renovation, and repair of the sanitary sewage works of the District, as authorized by Congress, and such amounts so advanced shall be reimbursed by the said Mayor to the Treasury out of money in the General Fund of the District of Columbia (including any special account therein).
D.C. Code § 34-2103