All the assessments on real property and easements shall be a lien against the property assessed from and after the first Monday in April in the year in which it is assessed and shall draw interest at the rate of nine percent per annum from May 1 of the year following said assessment, and such lien is not removed until the assessments are paid or the property sold for the payment thereof. It shall be the duty of the county treasurers to collect such assessments in the same manner as other taxes against real estate are collected, and the revenue laws of the state for the collection and sale of land for such taxes are hereby made applicable to the collection of assessments under sections 31-301 to 31-369. When bonds have been issued by the drainage district, the taxes so collected to pay the same shall constitute a sinking fund to be used for the payment of such bonds and the interest thereon.