Where is the bad smell come from

We did a job for a local cafe last week. There was a recurrent sewer gas smell that customer had been having a hard time tracking down.

We went there to locate the sewer gas leaking spot with a professional sewer gas detection equipment. Click the video link at Youtube to watch the whole interesting process.

Finally we found that the sewer pipe under the mop sink was disconnected and fixed the issue. Now customer is very happy!