Use this
http://www.diy.com/nav/fix/power-too...skuId=12028339
If you remove the lance and trigger from the hose, then cut off a piece of the hose about 4" long then re assemble the trigger and lance back onto the hose.
Remove the nozzle from the end of the lance and push the piece of hose over the end of the tube enough so it stays on.
You will now find the part of the hose that swells over the lance creates a nice seal in the sunroof drain hole.
I pressurised the bottle with air first to blow the crap out of the drain tube then after it cleared I then filled the bottle with warm soapy water and flushed the drain lines out with a few litres of water.
If all my ramblings is not making sense let me know and I will take photo's of my set so you can see what I mean.
Good luck