Didn't know were to post this.
My 99 Caravan van has a leak at the overflow tube o ring. There is a quick connect at the top of the fuel tank. It leaked when I completly filled the tank Why is there a overflow tube? Can't air can get into the tank, won't the gas evaperate, in 100 deg. weather?

 

Its not an overflow. Probably an evap emmissions thing but its hard to tell from your description. Id go to the dealer parts dept and see if the o rings are available. Be sure to ask if they see this problem and if there is a fix other than just o rings.

 

See where the 1/2 " tube ends, that's where the o ring leaks. What's this pipe called ?

 

It doesn't matter what it's called. The dealer can pull up a diagram, you point at the part you need. Just describe to them what you did here.