Overflow Hose

I just bought some at autozone that fit. At first the guy grabbed some thick stuff like you said, I think it was probably fuel line. I saw near it something with the same interior diameter but thinner wall marked as vac or emission line. I got that thin stuff instead. I think it was 3/8" ID. They sell it by the foot. This was one a 68 318 but I don't think it would be different.