“How is it “stealing” if it’s left on the curb? Sounds to me like people are making use (and money!) of someone else’s waste.”
Because firms such as restaurants have contracts with a disposal service to get rid of their kitchen grease. (Dumping it down the drain is a BIG no-no...first because it’s illegal, second because it plugs up the grease trap faster.) The disposal companies leave a closed pickup container outside the building alongside the garbage dumpsters.
As to the vacuum question, the disposal services use a vacuum truck to empty grease dumpsters and undersink grease traps. Take it from somebody with experience...you DON’T want to be standing downwind of one of those when it’s doing its job!!!