Thanks to David for this preparing this page. Essentially propane and butane are interchangeable as far as the user is concerned. No carburetor or appliance flame adjustments are necessary when switching between the two gasses.
Bleeder valves and vapor escape hoses are non-existent.
When plant personnel loosen the connection after filling raw liquid escapes copiously. Therefore extinguish all potential sources of ignition before driving up to the dispenser. Prices are posted on the side of the truck for Domestic fuel. If you are going to be the area for awhile, save the receipt from the gas purchase. The trucks have no onboard pump.