How do I mask out this pipe so that the arrow ONLY on the outside?

[beths95775902]

I'm trying to animate this arrow correctly and I can't figure out how to make the mask work the way it should. I'm not supposed to see the arrow when it's inside the tube, but when it comes out of the opening at the top, it should be visible on the OUTSIDE of the tube and down into the tube below. I'm not sure how to accomplish masking this so that I can still see the arrow when it's supposed to be on the outside of the tube.

HELP please!!