That person holding the position of supervising plumbing inspector, and that person holding the position of assistant supervisor of plumbing, and those persons holding the positions of plumbing inspectors, must successfully have passed the examination of licensed master plumber as given by the Board of Plumbing Supervision: Provided, however, That those men holding those positions, upon the passage of this act, shall not be affected thereby, so long as they shall continue in their employment.
53 P.S. § 15330