Drain odor following installation of push button.

[Jimyaks]

Recently replaced friend's pop up drain with a push button type and she complains of bad smell when she first uses it in AM but goes away after running water. It has an overflow vent. Any thoughts.

 

[Geofd]

Recently replaced friend's pop up drain with a push button type and she complains of bad smell when she first uses it in AM but goes away after running water. It has an overflow vent. Any thoughts.

Have her shine a flash lite into the drain if possible to see if the trap is dry have her clean the over flow (vinagar, clr) see what happens