The county treasurer shall be the custodian of the funds of the drainage district. He may designate 1 or more of his deputies who may act for him in the performance of any of his duties under this section. The drainage board may require the county treasurer and any deputy county treasurer so designated to furnish a bond payable to the drainage district, in addition to any bond payable to the county, conditioned upon the faithful discharge of his duties in respect to moneys belonging to the drainage district, the premium thereon to be paid by the drainage district. Moneys held by said treasurer shall be paid out only upon order of the drainage board, except that no such order shall be required for the payment of principal and interest on bonds.