On the back side of the engine.Its visible with the engine cover on. Right next to the breather hose on a 2001 2.8l 30v. Its short and looks like the letter F with 3 hookups one of which is on the bottom. Another hose runs off of it that goes through the plastic firewall to the brake resevoir. I have 2 part #s. One is 027133734E and another is pxo416509aem but I cant find it on the web. Thanks.

 

Its probably just called a hose. 027133734E is the actual audi part number. Unfortunatly an item such as that is probably only going to be availabe at a dealer. You may want to search some of the junkyard sides thou.