When suction on one breast—from a nursing baby or a pump—triggers a letdown in the other breast, the Haakaa collects it well. This simple, sock-shaped collection vessel works by suction. You squeeze the bell-shaped collection vessel, position the shield over the nipple, then release the base. Many people find that the lightweight silicone pump holds itself in place, hands-free. The milk collects in the bell below, then pours easily into another container.