The day before yesterday, I had a customer with a very foul smell coming from a guest bathroom. The homeowner had no clue as to why the bathroom would smell because it hadn’t been used in several weeks or even months.
Once I went through each fixture to make sure they worked, I discovered that the P-Trap for the shower had gone completely dry because the water had all evaporated due to lack of use!
So, with no water in the P-Trap, sewer gasses from the rest of the house were free to make their way up and into the living space instead of just going up the vent as would be normal!
Lesson: Make sure you run water through all your fixtures on a regular basis to ensure you keep your P-Traps full of water. This simple device performs an amazing function; it essentially provides a sewer gas barricade against the nasty smells you never want to smell inside your house!