sometimes you just need to vent, it's ok. both underbed tanks i installed i hooked up a vent hose. i used a filler neck off of a older 50's chevy truck for one and another that i dug out of a junk box at a body shop. both had vent conection on the filler neck. that one you got is just too dang fancy!! i had a heck of a time finding the propper size filler neck to match the tank input connection so i just had to use what i could find. seems like it was 1 3/8" or something, smaller than filler neck off behind seat tank. i actually used a 1 3/8 freeze plug as a gas cap for a while.