Sewage system odours inside can show a dry catch, broken vent

https://classes.iwcc.edu/eportfolios/296/home/common-plumbing-leaks-that-occur-in-homes

Sewage system odours inside can show a completely dry trap, broken air vent, or partial obstruction; Geelong buildings with huge trees or older sewer lines may need CCTV examinations to locate invasions and prevent repeating smells.