Air duct inspection service call. Televised ducts under slab floor from plenum area and register. Ran water in bathtub and see water coming into ducts. Ran water in kitchen sink and other sinks and also see water entering ducts. Believe that the main sewer line is leaking and getting into ducts. Recommend air duct repair and sewer line repair. Will provide a proposal for both lining sewer and ducts once the sewer is fixed.