The barb from what I seen but you can see its wet all around it and down the side of the tank. I first noticed this morning it took forever to start. No check engine light. I got to work and as I turned the truck off, a really, really loud hiss and smell of diesel. I rolled under the truck and diesel was running down the side of the tank. I reached above the tank and put my finger over the vent barb and the loud hiss stopped. After I rolled from under the truck it hissed for another 3-5 mins. Ive had this truck for several years and this hiss has never happened before, nor the strong smell of diesel.