The flamethrower is a homemade weapon, a propane tank with a bike brake for a trigger, found in a loading dock at the University of Eastern Colorado in The University. It is the strongest tool against groups of infected and bloaters, at the cost of short range.
Its workbench upgrades include reload speed.
Burn bloaters to strip their armor, then keep your distance, since a burning bloater can still grab you. Lure stalkers in and torch them as they close. Upgrade range first so you aren't standing in grabbing distance. Unlike a Molotov, it has no splash fire.