After we installed a new sewer system for the customer they noticed a faint sewer smell coming from underneath the hall lavatory sink. Upon arrival i smelled a fainted sewage smell under the lavatory sink, I noticed a loose lavatory faucet. Ran the camera as a customer service call as part of our warranty in case there is a break in the sewer line that we installed. Recorded the video and attached to the job, I found no breaks or sewage backups at all in the sewer line. I noticed the p-trap assembly was new and the trap bend had a white film stuck in it and smelled of sewage, the other connections did not smell at all. I cleaned the fitting and verified with the customer that the smell seemed to be the same as the initial smell. I filled the lavatory sink and when i drained it i noticed the pop-up assembly was leaking, I tightened down the assembly and tested again without any leaks. Last course of action was to shut the lavatory sink door and waited 10 minutes, upon opening the door i