If the estimated cost of the main sewer or drain of said system now or hereafter constructed shall be relatively large as compared with the estimated cost of the lateral sewers or drains tributary thereto, or if the said main sewer or drain shall be so located that it will or may receive the sewage or drainage from two or more districts, the governing body shall have power to pass an ordinance providing that the cost of such main sewer or drain below a certain designated point shall be borne by the city and paid in the manner provided in Kan. Stat. Ann. § 12-624 for the payment of the cost of main sewers and drains now or hereafter constructed beyond the corporate limits of the city. If the said main sewer or drain shall be so located that it will or may receive the sewage or drainage from two or more districts, the governing body shall have power to pass an ordinance providing that the cost of such sewer or drain below a certain designated point shall be divided among the said districts as nearly as possible in proportion to the benefits which the respective districts will eventually receive from the use of the said sewer drain, and that the proportion of the cost assigned to each district shall be assessed against that district in the manner provided by law: Provided, That the said ordinance shall state the point in the line of the main sewer or drain below which the provisions of this section shall apply, shall describe the proposed location of the said main sewer or drain from the said point to the outlet of the same or to the city limits, and shall state the manner of payment of the cost of the said main sewer or drain, whether by the city or by the tributary districts, and if by the tributary districts shall fix the proportion of the cost to be assessed against said district: Provided further, That any land within the corporate limits of any city which land is served by county or township sewers shall not be subject to assessment as herein provided.