Traps can be useful for catching rabbits, cats, gophers and more but in plumbing a trap is used for an entirely different purpose.
A drain trap is supposed to trap something you definitely do not want in your home... sewer gas. Sewer gas can creep into any room that has a connection to the plumbing system. The gas smell can be hard to pinpoint because most people are not used to smelling it, they just know it is not pleasant.
If you have an unpleasant odor in your house that you can't explain do an inventory of all drains and inspect them. To make sure the drain traps are doing their job you just have to make sure there is standing water in every drain.
- Sinks (Kitchen & Bath)
- Washing machines