Is it the Fuel Filter?

[reelapeelin]

Mudda the vent allows air into the tank as the motor pulls gas out of it...it's like puttin' your finger over the end of a straw with water in it...it won't come out until you remove your finger and allow air into the other end...vent will be a smaller hose that runs to the top of the tank from a fitting outside you hull somewhere...do you open a vent on top of your portable tanks?... ;) :)...

I went back and looked at the pictures you posted of your boat...there is something that MIGHT be the vent fitting under the rub-rail on the port side...that's the left if you're at the wheel and facing the bow...look under the rub-rail and tell us what that is... :)...