Good question! I replaced mine since it was old and brittle and kept breaking. (Sound familiar?) I hadn't realized it was only in the tip. I know it is part # 96611017000 and costs just over $100. I understand the venturi principle. I too would like to know what a hundred plus dollar plastic tube, that I had to replace, does in my car!
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James now has: 2008 987S 6 speed
Crashed: 2010 987.2 pdk in speed yellow!

Sold to a cool racer chick: 2004 986 S
YouTube channel: the PORSCHE as seen by NewArt
www.youtube.com/channel/UCohdrH2xHTklM1thxk0KKOQ?