The drain smells after a long absence. Where do I start?

What you can do

If the drain is clear, add water to replenish the trap.
Clean the accessible strainer or removable insert according to its manual.
Note whether the smell returns after flushing the toilet or using another appliance.

A dry trap should stop letting smells through once refilled. Rapid recurrence needs further investigation.

Stop if smells return quickly, drains gurgle, joints leak or wastewater backs up. More chemical cleaner will not fix every cause.

NAPREMO can assess the trap and connection. In a shared building, report possible stack problems to the manager too.

Technical references