So that does mean that the problem is in the right side.......any guesses why cos Im sure there is another drain on the left side too??

I've been having this issue for a few weeks. This thread presents the solution in the clearest way I've seen. With the pics from the Club Touareg forum, I was able to get the drain on my passenger's side cleared in about 30 minutes. The driver's side isn't giving me trouble, but I'm going to get up in there anyway.

I just went through this after Hermine's rains and wanted to add some more detail for future troubleshooters. I was able to isolate the problem to the sunroof drains pretty quickly by pouring some water in the channel around the sunroof and watching it not drain. I then tried clearing the drain up using some weedwacker string but kept getting stuck after a few feet.

I then searched for the drain's exit location but didn't get anywhere. I pulled back the wheelwell liner but no luck. Turns out, the drain exits behind the firewall fairly high up in the engine compartment. The water then comes out another drain (pics at http://www.clubtouareg.com/forums/f7...ins-57187.html) behind the wheel liner. The location of the sunroof drain meant I couldn't get to the exit to try and clear it. So, knowing that compressed air can blow connections loose and cause more problems, I stuck a length of 5/16" OD tubing down the sunroof drain hole as far as it would go. I then gently applied compressed air hoping that routing the hose down there would allow the air to get to the blockage before causing any problems. This ended up working and I soon had water flowing down both front drain holes in the sunroof.

I do much the same thing with the sunroof drain on my Jeep Grand Cherokee (which a '17 Cayenne will soon be replacing). I have some clear tubing used for an oxygen mask (for COPD) left over from when my father-in-law came to visit. It's just narrow enough to slide into the drain hose and stiff enough to be able to push it. I use an air hose hose blow gun setup to deliver only a very limited amount of pressure.

No bursts, just a slow push of air. The good part about using the hose is it lets me get under the vehicle and see the output port as I send the air. If I don't see anything coming out I have to assume there's either a blockage or a break in the drain line somewhere.

This is the gun setup I use:
https://www.amazon.com/gp/product/B004GHKASA

What I discovered with the Jeep is they tend to use a corrugated kind of hose at a certain point along the way. This prevents the weedwacker string from going through. The oxygen hose seems to move through that section better.

I suppose there ought to be some other kind of flexible plastic that would be more suitable for this purpose, but I've yet to find it...

Be very careful when using high pressure air to clear roof drains. I posted the pic below to show the roof drainage routing.