Example · Everyday puzzle

A sour smell in the kitchen

Location and smell character carry the most information; "does it get worse when the extractor runs?" separates a drain problem from damp inside a cabinet.

现象 · QUESTION

There is a persistent sour smell near the kitchen sink — where is it most likely coming from?

已知线索 · CLUES5 条

Duration: about two weeks, worse in the evening
Location: near the sink, close to the base of the cabinet
Smell: sour, not sharp
Change: stronger while cooking, weaker with the window open
Ruled out: rubbish is emptied daily; the drain has been cleaned

可能性排序 · HYPOTHESES概率为估计，不是结论

1. A dry or poorly sealed trap letting drain air back inabout 40%

依据：Matches the location and the sour character; pressure changes when water runs or the extractor runs, consistent with "worse while cooking"

2. Damp inside the cabinet causing mould (wood, seals)about 25%

依据：Damp at the base, and the smell strengthens as evening temperatures rise

3. Residue in a waste disposal or dishwasher filterabout 20%

依据：Smell worsens after water is used, as with fermenting residue

4. A fridge drip tray or condensate poolingabout 10%

依据：If the fridge is nearby it can produce a similar sour smell; test separately

5. Something else (wall damp, outside air drawn in)about 5%

依据：Needs further evidence; not the first priority

怎么验证 · VERIFY

Open the cabinet, wait ten minutes, then smell — is the odour coming from inside?
Pour water slowly into the drain and watch for bubbles or a surge of smell
Check whether the trap still holds a water seal (unused floor drains and sink traps dry out)
Clean the fridge drip tray and compare

场景还原 · RECONSTRUCT

If the trap has lost its seal, the smell is drawn in whenever the drain is under negative pressure: it is mild at rest and spikes when the extractor runs or when water is used upstairs. That timing separates a drain problem from cabinet mould — mould does not respond to the extractor.

复盘 · REVIEW

Use "location + smell character" to narrow to drains versus cabinet, then one extractor comparison to separate them. In most cases, refilling the trap or replacing a seal resolves it.

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