A Büchner funnel can be made out of porcelain, glass or plastic. On the top there is a container with a hole in the bottom. This container is put on top of a Büchner flask with a hole in the top and a hole in the side. In between the container and the Büchner flask there is a piece of filter paper which lets through liquids but not any solids. Attached to the hole in the side there is a vacuum which sucks the air out of the Büchner flask. This means that when any mixture is poured into the top, the liquid is sucked through the filter paper and the solid is left stuck in the filter paper.