Hi,
I have a 2015 TTS roadster, and have had the same problem. The drain pipe becomes clogged up with leaves, and so forth. Which then overflows, into the rear of the passenger seat. Where the Amp for the sound system lives. What a great design NOT! I had a light bulb moment, which was why not try a sink unblocker! That Cleans out grease and all sorts of stuff. So after pouring half of the (£4) bottle into the water collecting tank, I watched it for a few minutes. Then glug, glug the blockage seem to slow give way. I left it for about 10 minutes, then poured Luke warm water down the pipe. It had really cleared it out, I was amazed this simple but effective trick worked. So don't pay alot of money to a garage, get a sink unblocker. I also did the other side for good measure.
