Get a refillable silver fire extinguisher, the kind that only puts out regular fires. You unscrew the top and fill it with 1/2 JP5(white kerosene) and 1/3 unleaded gasoline.

Remove almost all of the rubber hose, leaving only about 5 inches, plus the nozzle.

Take it to the gas station and fill it with air, it has a air stem like a bike tire.

Get a small plumbers torch that has a pull trigger and instant start igniter.

You now have a flamethrower, be sure to enjoy burning the fucker up. Have a real fire extinguisher nearby to put out the residual fire that this will ignite.