Drain odours inside can show a dry trap, cracked vent

https://learn.multnomah.edu/eportfolios/918/home/why-you-need-a-plumber-to-clear-blocked-drains

Sewer odours inside can suggest a dry catch, broken air vent, or partial obstruction; Geelong buildings with large trees or older sewage system lines may need CCTV examinations to situate breaches and avoid recurring scents.