http://nexflowair.com/drumangelvac_how_they_work.php Compressed air enters at point (A) and into the Drum Angel/Drum Pump unit (B) which is mounted onto a sealed metal drum via the small hole. An adjustable knob (C) controls whether he unit creates a vacuum inside the drum to fill the drum or pressure to empty the drum. The liquid enters or fills the drum through a tube assembly (D) inserted and threaded into the large drum hole. An elbow attachment (E) connects the tube assembly to the hose and attachment assembly (F) which collects or dispels the liquid. Various attachments are available for liquid collection and transfer.