adblue

Sorry if it's already been covered, but can anyone tell me what the rubber bung below the fuel filler hole is for? Is it covering another hole that could be utilised for water or something, or is it where the Ad-Blue would go on a Euro6 engine?

Instruction leaflet for VW AdBlue kit includes part number for useful filling hose.

Anyone know if the main diesel tank can be removed without removing the Adblue tank? It looks like it clears looking underneath but not sure that the main tank filler neck will foul the Adblue filler....

O.k, so as my Kombi has been upgraded from Euro 5 140 to Euro 6 150, I've now got Adblue to get my head around, so this is a question to those in the know- how long does the 12 litres last and what would happen if you run out of Adblue? Can the engine still run on diesel only? Bit of a noob...