The accumulator has a spring diaphram internally that maintains system rest pressure for a short period of time after the car is shut off. Both sides are exposed to liquid fuel and the diaphram travel back and forth during system operation. When the car is at rest the diaphram relaxes and returns to a rest position. When the car is started a small amount of fuel is pushed out as it re pressurizes. A leak would have continual fuel leakage from the vent line while running.
Bill