One of the commonest faults in plumbing is the use of drain-pipes of too large a calibre. Five, six and even eight inch pipes are used where a diameter of four inches would be ample. If a line of a dozen or more water-closets together is laid out, the soil-pipe is at once increased to five inches in diameter, as if even the simultaneous discharge of ten times that number could begin to fill the soil-pipe full bore! Supposing a continuous line of closets be set, say three feet apart from center to center, the four-inch pipe between each would be more than sufficient to contain and carry off the waste water discharged at each flushing independently of the rest, so that a four-inch soil-pipe, with proper pitch, is capable of serving an infinite number of water-closets. Indeed, it is large enough to carry off the household wastes of a small town. The result, then, of using a soil and drain pipe five, six or eight inches in diameter, is simply to create an enormous cess-pool throughout its entire length, and when we come to the ancient custom of using great square brick and wooden sewers in our cellars, we have the folly of the proceeding brought forcibly before our eyes. It is the same with the smaller waste-pipes. They should never be large than is absolutely necessary to serve their purpose.