Sizing Individual Waste Lines

The water closet, strictly speaking, has no waste. It is usually connected directly into the stack on a short as possible separate branch of its own by the use of a closet bend. The closet bend is 3 or 4 inches in diameter if made of cast iron or steel and 3 inches if made of copper.

Because lavatories are used for washing hair, loose hair is often carried down into the waste pipe, causing a stoppage. Lavatory drainage is improved by using a minimum number of fittings and by eliminating long horizontal runs. The minimum pipe size for lavatory wastes is 1 1/4 inches, but 1 1/2 inches is more satisfactory.

Urinals present a particular problem because cigarette butts, cigar stubs, chewing gum, matches, and so on are often discarded in them. These materials can easily cause a stoppage. For this reason, urinals should be equipped with an effective strainer. Size of waste pipe should be at least 1 1/2 inches for wall-mounted urinals and 3 inches for the pedestal siphon jet urinal.

Shower wastes seldom cause trouble since they have a relatively clear water waste flowing through them. The usual diameter of the waste pipe for a single shower is 2 inches if made of cast iron or steel and 1 1/2 inches if made of copper.

A domestic kitchen sink requires a 1 1/2-inch cast-iron or steel waste pipe. When a sink is equipped with a garbage disposal unit, a minimum of 2 inches is required for the cast-iron or steel drainage piping.

Table 7-5.-Maximum Loads for Soil and Waste Stacks Having Four or More Branch Intervals 7-7

There are two styles of service sinks (slop sinks): the trap-to-wall and the trap-to-floor. They are used for disposal of wash water, filling swab buckets, and washing out swabs. The trap-to-wall type requires a 2-inch or 3-inch waste pipe; the trap-to-floor, a 3-inch waste pipe. For both types, if copper tubing is used, a one size reduction is allowed.

Scullery sinks are large sheet metal sinks used for washing large pots and pans and for general scouring purposes. The large amount of grease that usually passes through a scullery sink makes a 2-inch waste pipe necessary.

Drinking fountains carry only clear water wastes and a 1 1/4-inch waste pipe is suitable. An indirect drain (covered later in this chapter) should be used.

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