Drain odours inside can show a completely dry trap, cracked air vent

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

Sewer odours inside can indicate a completely dry trap, cracked vent, or partial blockage; Geelong residential or commercial properties with big trees or older sewage system lines might need CCTV assessments to find breaches and prevent reoccuring smells.