(c)that in fixing the rate of which the tax is to be levied, regard shall be had to the principal that the total net proceeds of the tax shall not exceed the amount required for cleaning private and public latrines, urinals and cesspool and for providing, extending or maintaining public latrine and urinals, together with the amount required to meet the proportionate share of the cost of supervision and collection and the re-payment of and payment of interest on any loan incurred in connection with this purpose;
