Complaint Customer reported intermittent sewer odors in the master bathroom. Inspection & Testing No odor was present at the time of inspection. Performed a smoke test to identify any hidden leaks or broken seals. Smoke was observed pouring from behind the access panel at the plumbing wall, where the cast iron stack is located. Found large amounts of rat droppings inside the wall cavity at this location. Diagnosis Identified a break or defect in the cast iron vent stack inside the wall. Odors are likely escaping through this break and entering the bathroom. Next Steps Wall will need to be opened to access and remove the damaged cast iron stack. Recommend replacing the damaged section with PVC piping. Estimate will be provided to the customer for repair work.