Its a goretex membrane plug, so it's constantly self venting.
The easiest way to get hold of them and a housing in which to install them is to buy one from PeteC.
He lists them in the online shop over at swaylocks.
http://www.swaylocks.com/cgi/surfshop/page.cgi?g=Detailed/3416.html&d=1They are definitely the the way to go!
