1967 Plymouth Barracuda - Fuel tank not vented properly??????

I have the same problem with my 75 dart but it doesn't have the line running back. So my pukes out the filler hole. Iv got to get it fixed before I paint it. I thought I had it straighten out with the new tank and return lines but the last time I filled up the next day I could smell gas and right under the fill cap was wet.