341.070.  Inspector — qualifications. — Each city with a population of fifteen thousand or more in the state, shall by ordinance, within three months after the passage of sections 341.010 to 341.080, create an office of plumbing inspector, whose duty it shall be to inspect all plumbing installed and furnish a certificate of approval of the same.  Said plumbing inspector shall not have less than six years' practical experience at the plumbing business, and shall not be interested, either directly or indirectly, with any firm or corporation engaged in the plumbing business.  The salary of said plumbing inspector to be provided for by the respective cities.