or wherever water is needed. These pipes are small in diameter and can go unnoticed within

the thickness of a standard stud wall. The riser connects to a horizontal pipe that then con-

nects to a fixture.

The more challenging counterpart is the drain, which uses gravity to mobilize waste down to

the sewer connection. Drainpipes always travel downhill at a slope that is regulated by the

building code for different fixtures. The vertical drain that carries wastewater from sinks and

baths is referred to as the waste stack; its diameter is small enough to fit within a typical stud

wall. The drain that connects to toilets is called a soil stack; it is twice as large in diameter

and does not fit within a standard wall construction. Both the waste and soil stack must rise

vertically through a building to the roof for proper ventilation.