The plumbing and drainage of all buildings, both public and private, in each of the cities of this state, shall be performed by persons authorized under the rules and regulations adopted by the local board of examining plumbers, in conjunction with the board of health for plumbing and drainage, and all plumbing and drainage work shall be executed in compliance with such rules and regulations. And all repairs and alterations in the plumbing and drainage of all buildings heretofore constructed shall also be performed and executed in accordance with such rules and regulations; but this section shall not be construed to repeal any existing provision of law requiring plans for the plumbing and drainage of new buildings to be filed with any local board of health and be previously approved in writing by such board of health and be executed in accordance therewith, except that in case of any conflict with such plans, rules and regulations of the board of examiners, the latter shall govern.