Water supply shall be protected against contamination from sewage by the prohibition of any connection between sewage and water systems which provide the possibility of water contamination by means of back syphonage or direct connection. Air in enclosed spaces shall be protected against contamination from toxic, explosive, or disagreeable gases or vapors from a sewage system by providing leak-tight and substantial waste and ventilation connections, and liquid sealed traps on all plumbing fixtures discharging into any type of sewage disposal systems.