Sewage system odours inside can show a dry trap, broken vent

https://canvas.pasadena.edu/eportfolios/4924~6653/home/common-plumbing-leaks-that-you-may-experience-in-your-home

Sewage system odours inside can show a completely dry catch, fractured vent, or partial clog; Geelong properties with large trees or older sewage system lines might require CCTV inspections to locate intrusions and protect against repeating scents.