Sewer odours inside can suggest a dry catch, split air vent

http://photohistory.oregonstate.edu/works/half/the-importance-of-regular-plumbing-maintenance

Drain odours inside can show a dry trap, cracked air vent, or partial obstruction; Geelong buildings with huge trees or older sewer lines might require CCTV assessments to locate breaches and protect against reoccuring scents.