I don't think you understand. The tube in the diagram above is the VENT It MUST be to open air, or the tank will either have internal pressure or a vacuum, depending on temp, etc.
Yeah, what 67Dart273 said... else you will have problems!!! Take a can of pop, put a straw in it, seal the opening "around" the straw so no air can get in... now suck real hard... the can will collapse inward if you suck hard enough and/or you won't get much fluid out... Do you really want your new metal gas tank to do that? (IF, your fuel pump is powerful enough...) Else your engine starves for fuel !!!
I've never seen anything "dump" onto the ground from my cuda's vent tube! It vents air in while engine is running and fumes out if it's hot... The old car's fuel system will function fine... even if the EPA is not happy... but then again, they want to crush these cars anyway !