What are the steps i can take to diagnose what is causing the sewer smell in my house. I have a septic system outside. I have not had it pumped in 4 years however it was "inspected" a year ago. Before i potentially waste my money and have the system pumped, how can I eliminate the problem is not caused by other sources. Should i call a plumber?..a septic pump company? DIY? I assume the two things to check are the traps and the roof vent? Any way to test the roof vent (flush and wait to feel air pressure?)