Airbox leaking oil, only when parked in sun

[duckb0y]

Well, it leaked again today.  I was out there at lunch to see if it had leaked, and as I was talking to my buddy who parks next to me, we noticed a drip... not of oil mind you, but gas, from the vent tube.
Now I'm wondering why liquid gas is coming out of there.  I know my tank is air tight as when I open it sometimes it is pressurized pretty well.  I'm thinking maybe that tube is dirty, giving the appearance of oil but really the gas is just washing some grime out of the tube. 

I will try to flush it out.  Oh, a note, the tank of gas had about 90 miles on it, so it was nearly cashed.  I'd estimate a little over a gallon left inside.