HOW MANY LINES ON THE FUEL TANK

[BIG C]

hOW MANY LINES ARE THERE ON A FUEL TANK ON A 92 W250 4X4 ctd?
By this I mean how many lines come out of the big cap on top of the tank?
mine has 2 that I think are for the pickup tube and a return.
There is also a small unit on the cap that I guess is a pressure relief valve, it has a barb fitting on it but no hose connected to it.
Should there be a hose connected to it and where would it come from.
Finally coul this missing hose be the cause of my trucks grey/ white smoke?
thanks

[BobS]

The tank has 2 lines; outlet & return. This is not counting the filler and the filler vent hose which both go to the filler neck.

[PToombs]

The small port is the Rollover Vent Valve. It lets the tank vent, and shuts if the truck rolls over. IIRC, someone posted someplace that that plastic cap is an oversight on the installers part, it should be removed. I wish I could remember where I read all these bits of info, but the alcohol has killed a few brain cells.