A distant fixture released a large flow
The noisy sink was not the fixture creating the pressure event.
↓House Autopsy · drain-waste-vent
The gurgling drain with a roof-vent cause
Several traps moved when another fixture discharged because the drainage system could not admit air correctly.
Trigger conditionlarge fixture discharge
Four layers, one connected story.
The vent path could not equalize pressure
Air was pulled through water seals instead.
↓Traps gurgled and water levels shifted
The timing linked multiple fixtures to one system event.
↓Vent inspection separated it from a local clog
Clearing the vent restored quiet drainage without treating each trap separately.
Canonical connection
The symptom and cause are separate objects.
The autopsy preserves how evidence connected them without collapsing uncertainty into one magic answer.
Several traps moved when another fixture discharged because the drainage system could not admit air correctly.
The visible symptom was the final chapter
The investigation followed the source, transport path, affected material and verification step separately.
What changed the direction
Timing and location evidence ruled out attractive but weaker explanations before repair work began.
The durable lesson
Repair the controlling source and then verify the outcome under the conditions that previously triggered the symptom.
Source→Path→Damage→Verify
