This act shall be liberally construed, to encourage the improvement of natural watercourses, to protect lands from damage and injury by overflow, and promote the public health, convenience, and welfare; and the collection of general or special taxes or assessments levied under the provisions of this act shall not be defeated by reason of any omission, imperfection or defect in the organization of any drainage district or in any proceeding accruing prior to the issuing of any bond or the confirmation of the report of the assessors of any special assessment, and no suit to set aside any general or special tax or assessment or to enjoin the making or collection of any assessment or installment thereof, and no defense of any kind to the validity of any improvement bond or assessment to pay the same, shall be allowed unless brought within thirty days after the confirmation of the assessors’ report.