There is, without fail, a TSA flunky in charge of piling up the Grey Tubs, once the screened “items” are removed. That person then has to lift the Tubs, carry them back to the front of the line, and set them down again (as noisily as possible, evidently, and usually whilst yelling things everyone already knows, even if some folks are way closer than earshot).
Here is how it works in Germany: a security person lifts the Tub post-security (also grey over there) about half a foot, turns it on its side, and the Tub rolls itself down a small, unobtrusive band of wheels set on a perfect angle on the side of the security belt, back to the front of the security line where passengers can take one as needed. There are no huge piles of Tubs in everyone’s way, no electricity is used, and minimal manpower.
I may be guilty of positive stereotyping here, and I have noticed that this excellent idea has also been adopted in Spain, yet it seems the sort of simple yet brilliant innovation a German company or person would have thought up, so I am assuming it originated there.
One might wish that folks from the Transportation Security Authority had more chance to travel, glean some ideas from abroad, and improve their airports (and moods).