The Rosso twins are
Join Date: Oct 2011
Location: United Kingdom
County: Tyne and Wear
The aircon drain is located in the same rubber bellows that the scuttle drains through, it is about 20-40mm up inside the little bellows located on the bulkhead, if you can get your finger in you will feel a little metal tube with a serrated end coming through the bulkhead.
If the drain is blocked it can back up water from the condenser and cause it to empty into the cabin, but there was also a design fault somewhere in there that was repaired by Alfa if it caused an issue, but I could never find what the official fix was.
I fitted a new drain tray to mine as whenever I drove abroad the footwell got flooded when the aircon was running a lot, but TBH it was a total pain of a job (dash out) and if someone knows an easier fix then I hope they tell you as I could never find another way of doing it.