V. Tanker was assigned to do draining (sucking) of oil inside station. After completing the oil sucking work, Permit Holder decided to remove the V. Tanker from the location to go to PDO Waste Management yard for draining (unloading) of the oil in this process, Permit Holder removed rear wheel chocks. Due to this V. Tanker suddenly started moving downwards on the slope of the ramp where it was parked and hit the fire hydrant line causing damage to the hydrant line and hose reel box.