The standpipe in the center of the canister has a 1/16" orfice halfway up the pipe that keeps the filter from draining all the way and also controls the rate of flow through the filter when the engine is running. The canister won't drain below that point. I've opened up filters on engines that haven't run in 20 years or more and they're still half full of oil.
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!