I will throw in my 2.74c here.
I have never seen Billyray50's problem in person, but I did camp next to him one night :).
When he pushed the 1/2" hose into tank fill line, I bet it went all the way into tank entrance, now the Larger fill tube is acting as the vent tube since the actual fill is through the 1/2" inner house.
The say way a coax hose that are now used at gas station pumps works. There is an inner hose that delivers the product (fuel) and outer hose is the vent of fumes back into the station vapor recovery system.