Could be the good ol' propane and jellied gas combo.
Basically, you have a regular propane bottle, only with a second valve that leads into the tank with a tube going to the bottom. The tank is filled with 90% jellied gas (essentially napalm) and 10% propane. The propane sits on top and its vapor pressure forces the gasoline out the bottom through the tube, while the propane siphoned from the top supplies fuel for the pilot light.