(1) At the time of retirement, members may purchase an optional actuarially equivalent life annuity benefit from the Washington state patrol retirement fund established in RCW 43.43.130. A minimum payment of twenty-five thousand dollars is required.

(2) Subject to rules adopted by the department, a member purchasing an annuity under this section must pay all of the cost with an eligible rollover, direct rollover, or trustee-to-trustee transfer from an eligible retirement plan.

(a) The department shall adopt rules to ensure that all eligible rollovers and transfers comply with the requirements of the internal revenue code and regulations adopted by the internal revenue service. The rules adopted by the department may condition the acceptance of a rollover or transfer from another plan on the receipt of information necessary to enable the department to determine the eligibility of any transferred funds for tax-free rollover treatment or other treatment under federal income tax law.

(b) "Eligible retirement plan" means a tax qualified plan offered by a governmental employer.