Each year during the existence of the district and at least 30 days prior to the making of the general tax levy for city purposes, the city engineer shall furnish to the city council an estimate of the expenses for the next year of the items of maintenance and operation provided for in the final resolution. The first year the engineer shall not make an estimate but the estimate in the final resolution shall be used. The city council shall at the time of making the next general tax levy in the city and in the manner provided for the general tax levy, levy a special assessment tax upon all the lands, exclusive of improvements, within the district which will be sufficient to raise that percentage of the total sum required in the estimate which is to be raised from the district.