I would think that the way it is setup in your situation is so the machine uses those two lines coming from the gear pump as both to/from depending on which way you are steering. Leaving the tank line to only let a little bit of fluid release when a shock is given to the system, as in steering left and all of a sudden wheel hits a rock giving the steering a jerk. Similar to how the drive motor would be. I have nothing to back up this line of thinking though other than common sense so I could be way off.