Sewage system odours inside can suggest a dry catch, split air vent

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

Drain odours inside can indicate a completely dry catch, cracked vent, or partial obstruction; Geelong buildings with large trees or older sewage system lines might require CCTV examinations to find invasions and prevent repeating smells.