Wash. Rev. Code § 54.04.140
Any person affected by RCW 54.04.130 who was employed by the private utility at the time of acquisition may, at his or her option, apply to the district and/or appropriate officers, for admission to any plan available to other employees of the district. Every such person who was covered at the time of acquisition by a plan with the private utility shall have added and accredited to his or her period of employment his or her period of immediately preceding continuous service with such private utility if he or she remains in the service of the municipal corporation until such plan for which he or she seeks admission becomes applicable to him or her.
No such person shall have added and accredited to his or her period of employment his or her period of service with said private utility unless he or she or a third party shall pay to the appropriate officer or fund of the plan to which he or she requests admission his or her contribution for the period of such service with the private utility at the rate provided in or for such plan to which he or she desires admission, or if he or she shall be entitled to any private benefits, as a result of such private service, unless he or she agrees at the time of his or her employment with the district to accept a reduction in the payment of any benefits payable under the plan to which he or she requests entry that are based in whole or in part on such added and accredited service by the amount of benefits received. For the purposes of contributions, the date of entry of service shall be deemed the date of entry into service with the private utility, which service is accredited by this section, and the amount of contributions for the period of accredited service shall be based on the wages or salary of such person during that added and accredited period of service with the private utility.
The district may receive such payments from a third party and shall make from such payments contributions with respect to such prior service as may be necessary to enable it to assume its obligations.
After such contributions have been made and such service added and accredited such employee shall be established in the plan to which he or she seeks admission with all rights, benefits, and privileges that he or she would have been entitled to had he or she been a member of the plan from the beginning of his or her immediately preceding continuous employment with the private utility or of his or her eligibility.
RCW 54.04.140