daddy, where do gas tank vent hoses go?

[edpdx]

Well I have been trying to figure out why the 73 c20 I drive wont allow a decent fill in either mid chassis tank. I don't get to pump my own gas here in Oregon, so I have to rely on the professionalism of the attendant. When the station is busy, I take what he can get in before it burps gas all over the tarmac. When they are not busy, a gut that know his way around the various problem truck and nozzles MAY use his skills to get the full tank I ask for, or he may just blow off his job and ram it, jam it, and scram it...dammit!

So... I have read in various forums that my problem is: "the nozzle I am using at the moment has been engineered to deliver gas to aggressively for yesteryears cars (they just aren't what they used to be)", "It is a GM planned obsolescence", "The sender is bad", "the inside tube fell out of the filler neck", "The vent tube is blocked or either tube is collapsed". I don't want to drop the tank yet so I am going to try a couple of things first:

I noticed when I crawled under the truck that the driver side tank has two hoses (fuel line type) routed toward the switch-over solenoid. One goes to the appropriate inlet on the switch. The other line is just looped and hung up over the driveline. I guess this is the vent tube? It definitely comes from the gas sending unit. Should this just be "open" and not attached to something. I am guessing this may be the problem. If it is a venting hose and it became clogged with dirt or insects, this could be the reason that the tank keeps burping fuel and that I seldom get more than a half tank. ?!?!

What of the idea that one fellow gave me about the original Inner rubber hose that resides in the original metal filler neck having become dislodged? He says it would have been pushed loose into the tank sometime when I was trying to force a siphon tube into the tank. Anyone hear of this on a 73?

Any help you can give is truly appreciated!

Ed