Wash. Rev. Code § 85.08.430
After the expiration of said thirty-day period, payment of assessments in full, with interest to the next interest payment date which is more than thirty days from the date of such payment, may be made at any time; PROVIDED, That the aggregate amount of such advance payments in any year, together with the total amount of the assessments due at the beginning of said year, shall not exceed the total amount of the bonds which may be called in that year according to the applicable bond redemption schedule. The treasurer shall accept payments of assessments in advance, in the order tendered, until the limit herein set forth has been reached.
The assessments contained in the assessment roll shall bear interest from the expiration of the thirty-day period at a rate determined by the county legislative authority and interest upon the entire assessment then unpaid shall be due and payable at the time each of said installments becomes due and payable as a part thereof.
The assessments contained in said assessment roll shall be liens upon the property assessed, such lien shall be of equal rank with other liens assessed against the property for local improvements and paramount to all other liens except the lien of general taxes, and shall relate back to and take effect as of the date when the county legislative authority determined to proceed with the construction of the improvement as provided in RCW 85.08.220.
RCW 85.08.430
Liberal construction-Severability-1983 c 167: See RCW 39.46.010 and note following.