Random clear/white pipe resting on undertray

[cha1n]

As topic states, there is a small diameter clear pipe (call it 5mm or so off of the top of my head) that is under the engine, not connected at one end, just resting on the undertray. Any ideas what this could be for? Tomorrow I'll have a proper go at seeing where the other end leads but a quick tug shows it's connected to something.

P.S. Sorry or peppering this forum with threads at the moment, I don't think there's any more required for a little while (fingers crossed).

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Would probably help to know that it's a 2.0 HDI (DW10TD).