Originally Posted by rudaire
To those that have responded that they get a sound when popping the cap, do you still have the original cap on the boat as far as you know?
As far as I know I still have the original cap. My cap is sligtly different than the one pictured above. I bet mine is the same as yours. Mine does not have a grip round the Circumference. It is almost impossible to turn by hand, you pretty much need to use the tool.
I am not near the boat to get a picture of the cap. Do you have a picture?
As far as I can tell my cap wasn't designed to be a vent.
I filled up again this weekend and tried to pay more attention to the sound. I belive it is suction. If you only loosen the cap sligtly the sound can last for several seconds.