Aha. Now that I look at the how it all fits together it all makes
sense. That would also partly explain the huge difference between a
"dry fill" and a "drain and re-fill".

> No reason for you to fill it. It will fill on it;s own from the transmission. Just add more fluid to the trans as needed. In use, it almost completely filled. After shutdown a lot will drain back into the trans. That is why autos have the fluid checked with the engine running.