Sometimes the smell will just arise from the sink, and it would be easy to point out.
Realistically, all kinds of food get dumped and chopped in there where water cant reach.
Fill the drain with ice and it will grind and throw the ice inside.

Image by Mike Klimek via YouTube
Place the rubber retainer back onto the drain and press the switch.
Youll hear the foaming effect.
Wash it out with water.

Continue to watchMike Klimek tutorial on YouTubefor full instructions and details.
This video shows how to get rid of the nasty sewage smell.
However, theres always going to be some funky smell with all the foods being ground.
