Section 4A. Master plumbers, journeymen, or apprentice plumbers, regularly employed by cities and towns or by institutions or corporations that are not engaged in the business of plumbing, may install such plumbing or make such repairs as may be required on the premises and property owned or leased and occupied by such cities, towns, institutions or corporations, provided that all such work performed by said plumbers shall be in compliance with the pertinent sections and provisions of this chapter.