Except as provided in RCW
51.16.250, every employer not qualifying as a self-insurer, shall insure with the state and shall, on or before the last day of January, April, July and October of each year thereafter, furnish the department with a true and accurate payroll for the period in which workers were employed by it during the preceding calendar quarter, the total amount paid to such workers during such preceding calendar quarter, and a segregation of employment in the different classes established pursuant to this title, and shall pay its premium thereon to the appropriate fund. Premiums for a calendar quarter, whether reported or not, shall become due and delinquent on the day immediately following the last day of the month following the calendar quarter. The sufficiency of such statement shall be subject to the approval of the director: PROVIDED, That the director may in his or her discretion and for the effective administration of this title require an employer in individual instances to furnish a supplementary report containing the name of each individual worker, his or her hours worked, his or her rate of pay and the class or classes in which such work was performed: PROVIDED FURTHER, That in the event an employer shall furnish the department with four consecutive quarterly reports wherein each such quarterly report indicates that no premium is due the department may close the account: PROVIDED FURTHER, That the department may promulgate rules and regulations in accordance with chapter
34.05 RCW to establish other reporting periods and payment due dates in lieu of reports and payments following each calendar quarter, and may also establish terms and conditions for payment of premiums and assessments based on estimated payrolls, with such payments being subject to approval as to sufficiency of the estimated payroll by the department, and also subject to appropriate periodic adjustments made by the department based on actual payroll: AND PROVIDED FURTHER, That a temporary help company which provides workers on a temporary basis to its customers shall be considered the employer for purposes of reporting and paying premiums and assessments under this title according to the appropriate rate classifications as determined by the department: PROVIDED, That the employer shall be liable for paying premiums and assessments, should the temporary help company fail to pay the premiums and assessments under this title.