Performed smoke test on sanitary waste and vent. Ran smoke machine for about an hour while checking both attics and 2nd floor master bath. No signs of any smoke accumulation within any of the spaces. After further investigation within the attic above bathroom and closet, Technician found a fresh air vent about 18 inches away from our sanitary sewer vent. This could possibly be the cause of the sewer gas smell. Technician sealed off the opening with caulking and plastic and let homeowner know to let us know if smell returns tonight and tomorrow morning. During today's visit Technician did not smell any sewer gas fumes.