Do a search on on this forum or google and you'll find some good advice and instructions on cleaning the drains. I can't remember if my owner's manual tells you how. Here's an old old link:
http://986forum.com/forums/showthread.php?t=13132&highlight=drain
Also check the drain pan around the top while it's in the service position. On my 2000MY they are foam and one had a tear that was letting water into passenger side. Waterproof tape solved that.