Wash. Rev. Code § 85.08.480
The respective installments of assessments for construction or maintenance of improvements made under the provisions of this chapter, shall be collected in the same manner and shall become delinquent at the same time as general taxes, certificates of delinquency shall be issued, and the lien of the assessment shall be enforced by foreclosure and sale of the property assessed, as in the case of general taxes, all according to the laws in force on January 1, 1923, except as hereinafter specifically provided.
The annual assessments or installments of assessments, both for construction and for maintenance and repairs of the diking and/or drainage system shall become due in two equal installments, one-half being payable on or before April 30th, and the other half on or before October 31st; and delinquency interest thereon shall run from said dates on said respective halves of said assessments.
The rate of interest thereon after delinquency, also the rate of interest borne by certificates of delinquency, shall be twelve percent per annum. Certificates of delinquency for any assessment or installment thereof shall be issued upon demand and payment of such delinquent assessment and the fee for the same at any time after the expiration of twelve months after the date of delinquency thereof. In case no certificate of delinquency be issued after the expiration of four years from date of delinquency of assessments for construction costs, or after the expiration of two years from date of delinquency of assessments for maintenance or repairs, certificates of delinquency shall be issued to the county, and foreclosure thereof shall forthwith be effected in the manner provided in chapter 84.64 RCW.
The holder of a certificate of delinquency for any drainage, diking or sewerage improvement district or consolidated district assessment or installment thereof may pay any delinquent general taxes upon the property described therein, and may redeem any certificate of delinquency for general taxes against said property and the amount so paid together with interest thereon at the rate provided by law shall be included in the lien of said certificate of delinquency.
The expense of foreclosure proceedings by the county shall be paid by the districts whose liens are foreclosed: Costs of foreclosure by the county or private persons as provided by law, shall be included in the judgment of foreclosure.
RCW 85.08.480