A Büchner funnel is attached to the flask via a black elastomer adapter. The hose barb is connected via vacuum hose to a vacuum source such as an aspirator. The flask should be clamped before use or the hose will likely cause it to tip.
Cross section of a Büchner Flask. Note the hose barb pointing right for attaching a vacuum source.
A Büchner flask, also known as a vacuum flask, filter flask, suction flask, side-arm flask or Kitasato flask, is a thick-walled Erlenmeyer flask with a short glass tube and hose barb protruding about an inch from its neck. The short tube and hose barb effectively act as an adapter over which the end of a thick-walled flexible hose (tubing) can be fitted to form a connection to the flask. The other end of the hose can be connected to source of vacuum such as an aspirator, vacuum pump, or house vacuum.