Help needed - extra pipe from the injection pump? Where does it go?

Hi all,
Sorry if this is in the wrong place. I have just bought a 300tdi discovery engine apparently from a p reg. I am in the process of labelling pipes and wires etc and there is a black plastic pipe coming from the injector pump. Do you know what it is? It looks like it might be a drain pipe. It is the left most pipe as if you were looking from the front of the engine- left of the throttle body.
Thank you to anyone who can help
Oli

Pipes already connected ( from the injector pump) are feed from fuel filter, injector excess fuel pipes, and feed back to fuel tank. Thanks again

If it is attached to the alloy top cover by a banjo bolt then it is the boost pressure pipe from the turbo