Figure 8-25 shows the waste and soil pipes and. associated fitting symbols in a riser diagram. The arrow represents the direction of flow. If you notice, all the pipes are sloping towards the building drain. Figure 8-26 further shows the basic layout of a drainage system. The function of each part is as follows:

. FIXTURE BRANCHES are horizontal drainpipes connecting several fixtures to the stack.

. A FIXTURE DRAIN extends from the P-trap of a fixture to the junction of that drain with any other drainpipe.

.  SOIL AND WASTE FIXTURE BRANCHES feed into a vertical pipe, referred to as a stack. If the waste carried by the fixture branch includes human waste (coming from water closets or from a fixture with similar functions), the stack is called a SOIL STACK. If a stack carries waste that does not include human waste, it is referred to as a WASTE STACK. These stacks service all the fixture branches beginning at the top branch and go vertically to the building drain.

. A BUILDING DRAIN (also referred to as a house drain) is the lowest piping part of the drainage system. It receives the discharge from the soil, waste, and other drainage pipes inside the building and extends to a point 3 ft outside the building wall. (Most local codes require that the house drain extend at least 3 ft beyond the building wall, but a few local requirements range from 2 to 10 ft.)

. A BUILDING SEWER is that part of the horizontal piping of a drainage system that extends from the end of the building drain. It conveys the waste to the community sewer or an independent disposal unit. 

Figure 8-26.-Basic layout of a drainage system.

. A FLOOR DRAIN is a receptacle used to receive water to be drained from the floors into the drainage system. Floor drains are usually located near the heating equipment and in the vicinity of the laundry equipment or any unit subject to overflow or leakage.

. A CLEANOUT is a unit with a removable plate or plug that provides access into plumbing or other drainage pipes for cleaning out extraneous material.