If the county commission determines to proceed with the construction of district sewers it shall cause plans and specifications to be prepared by the sewer engineer and shall advertise for bids for said work by causing a notice to bidders to be published, at least two weeks prior to the date of receiving bids, in a newspaper of general circulation published in said county. All contracts for such work shall be awarded to the lowest and best bidder, but the county commission may reject any and all bids.