The standpipe in the center of the canister has a small hole that prevents the oil from flowing back to the crankcase too quickly. That would rob too much oil flow to the bearings, since a bypass filter is not in the main flow path between the oil pump and the engine. It bleeds off a small volume of oil, filters it, and returns it to the oil pan. You will need to pull the filter cartridge, clean the housing thoroughly because it will be about half full of oil when the cartridge is removed, and examine the standpipe closely with a bright light. The hole is hard to find, but it will always be there. A squeeze bulb turkey baster comes in handy for sucking up the residual oil, but don't borrow the one from the kitchen unless you have a death wish! Go to Wally World and buy one for the shop!
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!