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

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...

I hope to be heading up the plains soon! Do you get out there a lot? Oli