Drain costs must be paid upon order of the board by warrants signed by the chairman and one other member of the board. The warrants are payable from the proper drain fund and, upon maturity, are receivable by the treasurer for drain assessments supporting the fund. The warrants may be issued at any time after the order establishing the drain has become final and after incurring liability to pay for drain work to be financed by drain assessments and in anticipation of levy and collection of the assessments. Every warrant not made payable on demand must specify the date when it becomes payable. Demand warrants not paid for want of funds must be registered by the county treasurer or, if the water resource district treasurer is custodian of the drain funds, the water resource district treasurer and bear interest at a rate determined by the board, not exceeding eight percent per annum. Warrants of specified maturities bear interest according to their provisions at a rate or rates resulting in an average net interest cost not exceeding twelve percent per annum if sold at private sale, and may be issued with interest coupons attached. There is no interest rate ceiling on warrants sold at public sale or to the state of North Dakota or any of its agencies or instrumentalities. All drain warrants must state upon their faces the purpose for which they are issued and the drain fund from which they are payable. The warrants may be used to pay drain obligations, or may be sold at not less than ninety-eight percent of par value, provided that the proceeds of warrants sold are placed in the proper drain fund and used exclusively for drain expenses. Any unpaid warrants issued for the acquisition of right of way or the construction of a drain, including all incidental costs in connection with the acquisition or construction, must be funded by a bond issue within one hundred eighty days from and after the filing of the assessment of all costs with the county auditor as provided in section 61-16.1-28, but this requirement may not be construed as prohibiting the funding of warrants or the issuance of bonds after the one hundred eighty-day period.