To be perfectly sanitary, plumbing fixtures must be made of some non-absorbent, non-corrosive material that is not easily cracked, crazed or broken, and that has perfectly smooth surfaces to which soil will not adhere so firmly that it cannot be removed by a flush of water, Outlets to fixtures should be as large or larger than the waste pipe and should be unobstructed by strainers or cross-bars, so that the waste pipe will receive a scourging flush at each discharge of the fixture. Fixtures that are provided with stoppers for the waste outlet should have overflows to prevent water overflowing the fixture when the stopper is in place. Fixtures should be set open, that is, perfectly free from enclosing woodwork or other casings that would cut off light and air. They should be well supplied with water for flushing, and in public places the walls and floor where they are set should be lined with some non-absorbent material.