Some axle vents are incorporated into the bolt that holds the brass brake line junction block to one of the rear axle tubes. Those usually have a hose nipple for a rubber tube that ends up above the high water level of trucks that go off road.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!