The first large hose you spoke of is the fuel supply directly from the tank.(you were right in your assumption). The second small diameter hose is a return line from the accumulator. It is there on the nitrogen charged side of the accumulaor diaphram in case the diaphram inside fails. The hose will return the fuel to the main line and not cause a fire hazard. Be careful when servicing this yourself for this is an always pressurized system via the accumulator.