I thought it odd the upper container would be the clean product, since it would seem advantageous to make gravity do some of the work in the filter process. But maybe this does make sense, following the plumber's mantra that $#!7 flows downhill.
I heard the following story some 50 y ago. The night watchman of the lab felt thirsty. He entered a lab, opened a fridge and drank the cold water he found in a flask. Next day, the technician working in the lab (actually a vaccine-manufacturing facility) was aghast to find that someone had opened his fridge and nearly emptied out a flask containing a culture of typhoid bacilli.
Happily, nothing happened to the watchman.