converting exhausts into working flamethrowers.

ive seen a few pictures and videos on the internet where people hook up what looks like a propane tank and somehow run it to their exhausts or sissybar ends and shoot flames out the back of their bikes, does anyone have any idea where I can get more info on how to do that? I have a pretty vague idea but i want to see if anyone has any experience or can point me in the right direction. Ive spent a long time researching on the internet and cant seem to find any more info.  

The Mini Dragon looks like a simple setup. I suppose if you turn down the pressure on the tank, it will be more of a yellow bright flame. Otherwise, the blue flame will look good at night and makes an audible sound like a camping stove.