Well I think I found why the left rear area kept getting flooded at the slightest rain:
What a pain in the @$$ it was to fish that little thing out. Had to go from the bottom up and then fish it out of the foam buckets with one finger... without tearing the foam apart. Anyone know if it's a Boxster part or just some randon debri?
Do yourself a favor and get one of these trombone cleaners:
Better than anything else I have tried. Flexible enough to go around tight corners, stiff enough so you can push it without it buckling, and thick enough that you can twist and spin it around. Bend one of the tips on a couple of spots so that the end is slightly and gradually curved. That way when it catches on a ridge or corner you can spin it and the end will free itself. Some drains have tricky corners (front right especially) but with practice you'll find all the tight spots and learn to go around them quickly. Then when the tip comes out under the car pull the whole thing out from underneath. The bristles should leave your drains nice and tidy.
But now I have all seven drains (that I know of) fully working. Let's see how good the perform now...