How do i report suspected drug activity in my home?

I suspect that my brother may be dealing or doing illegal drugs in my house. I don't have any proof of this, but there fowl smell in the basement or garage whenever his friends come over. Its so bad that I have to cover ventilation or it will give me a headache. He claims it is just "incense", but I don't by it. My parents won't question him or do anything. What can I do to expose this issue and how should I report it to the authorities?