You can check my credentials to answer this question in this thread, second post down.......
Here

In reality, a police department is not going to help you with identifying the smell.

Even if he knew EXACTLY what the smell was, that does not tell him at all who is using.

Someone mentioned that you do not have to be accusatorial, and that is true. In my opinion though, you DO have to hand them a drug test that tests at a minimum heroin, cocaine, meth, and marihuana. Explain to them why you are handing it to them, and make them take it right then. Anything short of that is doing a disservice to your children. A parent's job is not to be their child's friend, it is to be their parent.

Off rant!