Drain odours inside can indicate a dry catch, broken vent

https://academy.educause.edu/eportfolios/12410/home/reasons-why-homeowners-trust-plumbers

Sewage system odours inside can suggest a completely dry trap, broken air vent, or partial blockage; Geelong residential properties with large trees or older sewage system lines may need CCTV evaluations to find invasions and avoid persisting scents.