i have two 16 gallon tanks. I think the second one was added on by the previous owner, scary. He only has one fuel line from tank #2 to #1, then from #1 to the fuel pump is one line. I have a second line from #1 that goes up to the fuel pump, but isn't connected, what is this, is it a return line? Is it a vapor line? Can i plug it? that just looks like a way for water to get into my fuel.