You don't.
Vacuum filtration flasks are connected to a vacuum source with the side arm, while a rubber seal and Buchner funnel (with filter paper) are fitted
onto the top part on the wider neck.
Vacuum sources can be a water aspirator or a vacuum pump.
http://oxfordchemserve.com/buchner-filtration-apparatus-70-m...
The flask by itself, no matter what you do with it, cannot generate significant vacuum.
[Edited on 6-2-2015 by blogfast25] |