How can you tell what drugs people are making?

I'm pretty sure that my neighbors are making drugs and i want to know what kind they are making. Every once in a while when there window is open you can smell a similar to a sewer coming from the window. Which will also go away after about 5 minutes of them closing their window. Also sometimes late at night you will see flashes coming from their porch and they will tell the kids to go away because it was not age appropriate. We told the cops about it but they don't care. How can i tell what they are making and what should we do about it? (I am positive they are making drugs because they seem to be on drugs 24/7)