Drain odours inside can show a dry trap, broken vent

https://telegra.ph/Leak-Discovery-101-Fixing-Hidden-Pipes-Issues-in-Geelong-Houses-04-17

Drain odours inside can suggest a dry trap, broken air vent, or partial obstruction; Geelong homes with large trees or older drain lines may require CCTV evaluations to situate breaches and prevent recurring scents.