The Expence of making any new Sewer shall be defrayed as herein-after provided by special Sewer Rates to be levied on the Occupiers of all Lands and Buildings within the Drainage District in which such Sewer is situated: Provided always, that where in the Judgment of the Commissioners, and by Allowance of the Inspector, any Lands or Buildings were sufficiently drained before the making of such new Sewer, the Occupiers thereof shall be entitled to have such Deduction made from the special Sewer Rates to which they would otherwise be liable in respect of the making of such new Sewer, and for such Time as the Commissioners, with the Approval of the Inspector, shall deem to be just, having regard to the Cost of making such new Sewer, and to the Value and Efficiency of such old Sewer; and whenever any old Sewer is enlarged, or open Sewer closed, the Expence of such Enlargement, or of closing such open Sewer, shall be defrayed in like Manner as if it had been incurred in making a new Sewer.