Smoke test

I was doing a smoke test on the Evap hose line (hooked up in the engine area) and noticed smoke coming out at the gas fill tube area. There are three hoses at the fill line tube. The regular gas line and a smaller tube next to it (not sure what they call it) but there is a, I guess about a half-inch hose attached to the gas fill line and after inspecting the area the half-inch hose was not connected to anything, just opened to the air, yet it was attached to the gas fill tube (side by side). I couldn't see anywhere that it would attach to. It's a tight area. I tried to follow the line and it appeared to go over the gas tank, but I couldn't say for sure.

Thanks for your comment.