In foreclosing local improvement assessment liens, a city or town shall proceed by filing a complaint in the superior court of the county in which the city or town is located. It shall be sufficient to allege in the complaint (1) the passage of the ordinance authorizing the improvement, (2) the making of the improvement, (3) the levying of the assessment, (4) the confirmation thereof, (5) the date of delinquency of the installment or installments of the assessment for the enforcement of which the action is brought and (6) that they have not been paid prior to delinquency or at all.