Water in the Tailgate

[Tyroaudi]

I have a '58 plate Limited Edition Avant and went to the car wash today. Nothing unusual just the normal spray cleaning fluid, pressure wash, clean with soapy mitts and a final pressure wash and microfibre dry.
However, when I got home and opened the tailgate there was a sound of water rushing through the internal of the tailgate. Open it - water flowing sound, close it - water rushing sound. I've never experienced this before and I've had another A6 Avant and an A4 Avant.
I know there can be issues with the rear washer leaking but when I've experienced that before it was obvious because of the fluorescent lime green colour of the wash I use, not this time.

My questions are:

!. Where can/does the water get in?
2. Is this as a result of an over zealous pressure washer operator?
3. How do I get the water out and stop it entering in the first place?

[Tyroaudi]

I think I have identified the issue.

Water seemed to be getting behind the tailgate rear light cluster where the foam gasket had gone quite hard. Replaced with new expanding foam strip (search eBay) and nothing since.

To get the water trapped inside out I removed the small bungs at the bottom of the tailgate. I've just stuck gaffer tape over them until I can get the proper part from Audi.

[54A4Avant]

Nice one. Thanks for updating with the solution, as this might help others in future.