Sewer odours inside can show a dry trap, cracked vent

https://online.seminolestate.edu/eportfolios/1186/home/why-you-need-a-professional-plumber-to-clear-blocked-drains

Sewage system odours inside can indicate a completely dry catch, broken vent, or partial blockage; Geelong homes with large trees or older drain lines may need CCTV examinations to find invasions and prevent reoccuring scents.