Anybody know the size of our oil drain valve? 18mm or 20mm want to change it to the fumoto oil drain valve but not sure of the size.

 

It's 18mm. For more information Click Here

 

It's an 18mm. I am using a Fumoto valve on my Jeep but as far as my Porsche goes, it sits to low for a Fumoto valve IMHO! I would just install a nice magnetic plug and not have to worry about tearing it off out on the highway.
http://www.lnengineering.com/drainplug.html

 

I would not chance it. I have one on my Jeep and my wife's Audi and have used them on allot of cars over the years. I also thought about for my 997 but there appears to be two issues. I would be afraid of it getting damaged and possibly losing oil because of how low the car is. And I think you might have a problem tightening it down as the drain plug sits flat in a bit of a cup. They are very convenient though when changing oil. Although on my 08 it really is pretty easy to do the oil and filter. Takes me longer to get the drain pan and tools I need then the actual oil change.

 

Pick up the LN Engineering magnetic plug and possibly the billet oil filter kit as well. I believe they offer this stuff in a bundle now.