On the euro early 911's, and some U.S. cars there is a fuel tank overflow box located underneath the front cowl on the drivers side. It's about 4-5 inches square. At the bottom there are 2 nipples. One is 9mm and the other 15MM. The 15 mm goes directly to the tank. the 9mm is the actual vent to outside.
The 9mm hose is available from the dealer, the 15mm is NLA. I am looking for the correct 15mm ID hose that is fuel vapor compliant.
I found a old post that said SM had it in stock. I called them and it was 16mm instead of 15mm they have, which would probably work. Then I asked if it was fuel vapor compliant. Silence on the phone. Then the salesperson said they would be willing to check with others and give me a answer and call back within 15-20 minutes. No call. So I assume they don't have it, or don't know.
You can go to Home Depot and buy what appears to be the real deal, but not fuel compliant. Being the 15 mm off the tank, a full tank will splash a little gas up the hose. Over a short time, the hose will start to melt. I googled the manufacture of the German dealer 9mm hose and they do have a U.S distributor. But, their online catalog showed hose only up to 10mm, and 100 meter rolls.
If anyone has some sensible thoughts, please share your source.