Plumbing shall be so sized, installed and maintained as to carry adequate quantities of water to required locations throughout the establishment, as to prevent contamination of the water supply, as to properly convey sewage and liquid wastes from the establishment to the sewerage or sewage disposal system, and so that it does not constitute a source of contamination of food, equipment or utensils, or create an insanitary condition or nuisance. (1961 code § 6.06.090.)