Ok, so I'm putting in EFI (port FI, 45lbs fuel pump required, not TBI which requires much lower pressure) in my 1973 K5, I have a 50gal Hickey Gas tank, which has already been Renu'ed. Being that it's already been epoxy coated, it's somewhat difficult to modify at this point. So, I need to add a fuel return line. Problem is, my tank has a 3/8 pickup out the front, a 3/8" vent out the side, the main filler and 5/8" filler vent and that's it. So if I use the vent outlet on the tank as the return inlet, how can I vent the tank, or does it even need vented? Does a fuel system need to be vented? I think so, but I'm not an expert here. From the factory it has a non-vented gas cap. But I belive that top vent tube was just plugged, but some hack before me could have done that. It did have a charcoal canister from the factory, but it was not hooked up when I bought the truck in '92. Whenever I removed the gas cap after a long trip, it would make a giant sucking sound, probably as air filled the vacuum created inside the tank. Would it be acceptable to tee in a vent line into the filler vent? Or possibly plumb the fuel return line into the filler vent? Where should I vent it to? Does it have to go to a charcoal canister? Can I just put a little breather on the vent line, providing I can find a method to vent the tank? BTW, thanks to advice from Paulmoon, who was burning up pumps with his EFI conversion, I decided to use this type of setup with a surge tank (swirl pot): http://www.sdsefi.com/techsurge.htm The surge tank has it's own vent, but that's already on the backside of a the low pressure pump, so it's not vented the tank. Thanks for any advice.