For the protection of streams flowing through United States government parks and reservations in the District of Columbia from pollution by sewage discharged therein from sewerage systems of Maryland towns and villages bordering said District, the Mayor is authorized to enter into an agreement with the proper authorities of the State of Maryland for the drainage of such sewerage systems into and through the sewerage system of the District of Columbia; and the said Mayor is further authorized to permit connections of Maryland sewers with the District of Columbia sewerage system at or near the District line whenever, in his judgment, the sanitary conditions of streams flowing into and through such United States government parks and reservations in the District of Columbia are such as to demand the elimination of such pollution: Provided, that all cost of construction of such sewers to and connection with the sewerage system of the District of Columbia shall be paid by the proper authorities of the State of Maryland, and that said State shall enter into such agreement with the Mayor and shall guarantee the protection of the District of Columbia sewerage system from unauthorized connections thereto, and shall reimburse the District of Columbia for the actual cost of pumping and handling such sewerage by annual payments for such service as determined by the Mayor in such agreement; all such sums collected therefor to be paid into the Treasury of the United States through the Director of the Department of Finance and Revenue to the credit of the District of Columbia.