A filter funnel is a funnel, often made of glass or porcelain, which contains an apparatus for separating solids from liquids. Buchner funnels are one kind of filter funnel, but filter funnels can also be fashioned from ordinary funnels by inserting filtration paper between the funnel and the receptacle.
Filter funnels work by catching large solid particles and allowing smaller liquid particles to pass through unimpeded. They are widely used in chemistry labs, auto repair shops, and illegal narcotics operations. Some U.S. states restrict the sale of glass filter funnels, due to their potential use in the manufacture of drugs.
Steel filter funnels are a common piece of workshop and auto shop equipment, used to remove debris from oil, fuel, and coolant. These metal funnels use brass or plastic filters that can be reused again and again. Glass filter funnels generally use disposable paper as a filter. Buchner funnels have multiple small holes in the base of the funnel's cup, serving as a filter.