It's about halfway down the center standpipe, usually in line with the inlet fitting on the side of the canister. Try installing the cap and the rubber gasket without a filter element, turn the canister upside down, and pour a solvent like Mineral spirits into the bottom fitting. Then use air pressure to blow the solvent through the hole to make sure it's not clogged. It's very small and hard to see.
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!