Mo. Rev. Stat. § 341.160
A "Board of Plumbing and Sewer Inspection" is hereby created which shall consist of one licensed master plumber who shall also be a licensed master drainlayer and one licensed journeyman plumber to be appointed by the county commission. The term of office of said two members of said board shall be two years. The county health commissioner and the supervisor of the department of plumbing and sewer inspection shall be ex officio members of the board. The master plumber shall act as chairman of the board and the supervisor of the department of plumbing and sewer inspection shall act as secretary of the board and shall keep a full and complete record of the acts and proceedings of said board and shall provide all applicants for a license under sections 341.090 to 341.220 with blank application forms. The board of plumbing and sewer inspection shall examine all applicants for a license to act as a plumber or drainlayer or to engage in the business of plumbing or drainlaying and shall adopt rules governing its organization and proceedings and shall have the power to revoke any license heretofore granted or granted by it. All persons heretofore licensed under the provisions of art. 2, chap. 143, RSMo 1939, shall be deemed to have been licensed under the provisions of sections 341.090 to 341.220 and no person may engage or work at the business of plumbing either as a master plumber or a journeyman plumber or a drainlayer without a license issued by the board of plumbing and sewer inspection. The members of the board shall meet at least once a month and shall each receive ten dollars for each meeting, to be paid by the county commission, except the health commissioner and the supervisor of the department of plumbing and sewer inspection who shall serve without compensation.
§ 341.160, RSMo