Sewage system odours inside can show a completely dry trap, fractured vent

https://learn.multnomah.edu/eportfolios/918/home/why-you-need-a-plumber-to-clear-blocked-drains

Sewage system odours inside can show a completely dry trap, fractured vent, or partial blockage; Geelong buildings with huge trees or older sewer lines might require CCTV evaluations to locate breaches and prevent recurring scents.