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

https://felixrbys875.image-perth.org/from-drips-to-calamities-a-geelong-plumbing-technician-s-tips-for-usual-household-plumbing-issues

Drain odours inside can show a completely dry trap, split air vent, or partial obstruction; Geelong buildings with big trees or older drain lines might require CCTV inspections to locate invasions and prevent repeating scents.