Engine gurus - How does the valley pan work? (N62)

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I have the N62 in my X. I have coolant issues but looking at all the photos diagrams I can't work out how the valley pan works.

From the photos it looks like there is one opening into the valley pan which is at the top and connects to the inlet of the water pump, so I can understand how under pressure coolant could enter the valley pan but how does the coolant circulate out of the valley pan?

I've put two photos in below - one with the valley pan, showing no exit points on the bottom of the pan and one of the valley pan cover showing the one entry/exit