Flamethrowers are relatively simple weapons that can be easily made, though they are inherently dangerous. This simple design would probably work; all that is missing is a special valve. I got the idea from a fire extinguisher. I had an old one laying around and I took it apart to use. I cut and welded together the pipe and frame you see, then screwed the extinguisher bottle in. An ordinary propane torch is strapped to the end to ignite the fuel, while the extinguisher trigger is welded to the other end.