Whenever the Board of Public Works and Safety determines that interceptors or traps are needed to protect the sewerage system or the operations of the wastewater treatment plant from grease, oil, sand or similar substances occurring in a customer’s sewage, such traps shall be installed by the customer on his or her own lines at his or her own expense. He or she shall maintain them so that none of such substances can be carried over into the public sewers. All traps shall be subject to the city’s approval as to construction, location and installation.