Drain pressure: normal venting versus trap disturbance investigation session

Drain pressure: normal venting versus trap disturbance

Record which fixture is used, where gurgling occurs, whether flow is slow, and whether trap water or odor changes afterward.

Browser-local draftNo session answers are sent to the server. Evidence balanceScores organize observations; they are not probabilities. No repair authorizationStop signals override the ordinary workflow.

Freeze the evidence

Record the condition before interpreting it.

Observed at Weather / equipment / water-use state First visible, audible or measurable change Location, direction and delay

Evidence ledger

Mark what raises or weakens each route.

Leave unknown items unmarked. Contradictory observations are useful evidence.

Partial branch or main drain restriction

Wastewater displaces air and creates pressure because the drainage path is narrowed.

Raises fit +2 eachSlow flow and gurgling togetherSeveral fixtures interactSymptoms worsen with larger discharge

Lowers fit −2 eachNormal flow with only wind-related odor

Notes for this route

Vent obstruction or inadequate venting

The drain cannot admit or release air through the intended vent path, so traps respond.

Raises fit +2 eachTrap movement with otherwise acceptable flowSymptoms across connected fixturesRoof vent condition is suspect

Lowers fit −2 eachA clear downstream backup or overflow

Notes for this route

Dry, siphoned or leaking trap seal

The local water seal is absent and odor enters even without a major restriction.

Raises fit +2 eachOdor at an infrequently used fixtureImproves after adding waterNo broad slow-drain pattern

Lowers fit −2 eachMultiple fixtures back up under load

Notes for this route

Decision points

Change one condition at a time.

An answer changes investigation order; it does not prove a concealed condition.

Are several fixtures slow or interacting during a large discharge?

YesNoUnknown

If yes: Move a shared restriction ahead of a local trap issue.

If no: Check venting and the affected trap seal.

Observed answer and evidence

Does adding water to an unused trap temporarily stop the odor?

YesNoUnknown

If yes: Document why the trap is drying or losing its seal.

If no: Continue with pressure interaction and restriction checks.

Observed answer and evidence

Safety interlock

Stop signals override scoring.

Mark the stop state when any listed boundary is present. Do not create a better clue by increasing exposure.

Do not mix drain chemicals or add a product after another chemical has been used.
Stop and call a professional for sewage backup, repeated overflow or inaccessible vent work.

A stop signal is presentPause ordinary investigation and arrange an appropriate competent or emergency response.Safety note

Current conclusion

Explain what changed the ranking.

Leading pathway and why Strongest competing pathway Evidence still missing Smallest safe next action / handoff

Drain pressure: normal venting versus trap disturbance

Record the condition before interpreting it.

Mark what raises or weakens each route.

Partial branch or main drain restriction

Vent obstruction or inadequate venting

Dry, siphoned or leaking trap seal

Change one condition at a time.

Are several fixtures slow or interacting during a large discharge?

Does adding water to an unused trap temporarily stop the odor?

Stop signals override scoring.

Explain what changed the ranking.

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