DEFINITIONS Sections 201–202

The unobstructed vertical distance through the free atmosphere between the lowest opening from any pipe or faucet supplying water to a tank, plumbing fixture, or other device and the flood-level rim of the receptacle.

The unobstructed vertical distance through the free atmosphere between the outlet of a water supply pipe and the flood-level rim of the receptacle into which it discharges. Minimum 2× pipe diameter, never less than 25mm.

Accepted by the Administrative Authority as meeting the requirements of the Code, or as complying with standards adopted by the Administrative Authority.

The individual official, board, department, or agency established and authorized by a state, county, city, or other political subdivision of the state to administer and enforce the provisions of the Plumbing Code as adopted or amended.

A device attached to or a part of the plumbing system that performs a defined function but does not, in itself, receive or discharge waste. Examples: vacuum breakers, pressure-reducing valves, backflow preventers.

The flow of water or other liquids, mixtures, or substances into the distributing pipes of a potable supply of water from any source other than the intended source. Caused by back-siphonage or back-pressure.

A device or means to prevent backflow into the potable water supply. Types include: reduced pressure zone device (RPZ), double check valve assembly (DCVA), atmospheric vacuum breaker (AVB).

A device installed in a drain or pipe to prevent overflow from backing up into a lower level when the public sewer is surcharged. Required in floor drains or fixtures below the overflow rim level of the nearest upstream manhole.

Any part of the piping system other than a main, riser, or stack. A branch receives the discharge from one or more fixture drains and conveys it to a larger pipe.

A length of soil or waste stack corresponding in general to a storey height, but in no case less than 2.4 m (8 ft), within which the horizontal branches from one floor or storey of a building are connected to the stack.

A vent connecting one or more individual vents with a vent stack or stack vent. Runs horizontally, must pitch back toward the drain at a minimum 2% slope to prevent liquid accumulation.

That part of the lowest horizontal piping of a drainage system which receives the discharge from soil, waste, and other drainage pipes inside the walls of the building and conveys it to the building sewer beginning 0.6 m (2 ft) outside the building wall.

That part of the drainage system that extends from the end of the building drain and conveys its discharge to a public sewer, private sewer, individual sewage disposal system, or other point of disposal. Begins 0.6 m outside the building wall.

A device, fitting, or assembly of fittings installed in the building drain or building sewer to prevent the circulation of air between the drainage system of the building and the building sewer or public sewer system. Now generally prohibited — use individual fixture traps instead.

A branch vent that serves two or more traps and extends from in front of the last fixture connection of a horizontal branch to the vent stack. Used in battery-venting arrangements to reduce the number of individual vent pipes.

An access fitting provided in a drainage pipe to allow for rodding or cleaning. Must be accessible, same size as the pipe it serves (up to 100mm), and installed at changes of direction and at intervals not exceeding 15 m on horizontal runs.

A single vent pipe that connects at the junction of two fixture drains and serves as a vent for both fixtures. The two fixtures must be on the same floor level and drain into the same horizontal branch.

A pipe inside the building that conveys storm water from the roof to the building storm drain, combined building sewer, or other approved place of disposal. Also called a downspout or leader (inside).

A point on a backflow preventer or vacuum breaker established by the manufacturer and indicated on the device by a mark "C-L" or comparable designation. The device must be installed so that the C-L is above the flood level rim of the fixture served.

Any physical connection or arrangement between two otherwise separate piping systems, one of which contains potable water and the other water of unknown or questionable safety or steam, gas, or chemical. Through this connection, contamination may flow into the potable water system.

A drain from two or three fixtures connected to a single trap. Commonly used for multi-basin kitchen sinks where both basins drain to one trap and one drain outlet.

A branch leading from a soil, waste, or vent pipe, building drain, or building sewer that is terminated by a plug, cap, or other closed fitting. Dead ends are prohibited in drainage and venting systems as they create stagnant zones and odor traps.

The length of a pipe measured along the center line of the pipe and fittings — following the actual path the fluid travels, including all bends and offsets. Used in pipe sizing calculations and for determining maximum vent distances.

Unless specifically stated, refers to the nominal diameter as designated commercially. The nominal diameter of a pipe does not equal the actual inside or outside diameter — it is a trade designation. Always verify actual ID/OD in pipe standards (ASTM, PNS).

Any pipe which carries waste water or water-borne wastes in a building drainage system. Distinguished from vent (carries air) and supply (carries potable water under pressure).

All the piping within public or private premises which conveys sewage, rain water or other liquid wastes to a point of disposal — but does not include the mains of a public sewer system or private or public sewage treatment or disposal plant.

Any vent that does not carry water or water-borne wastes. The most common type of vent in a plumbing system. Distinguished from a wet vent, which simultaneously functions as both a drain and a vent pipe.

The minimum cross-sectional area at the point of water supply discharge, measured or expressed in terms of the diameter of a circle. Important for calculating air gap requirements for vacuum breakers and hose connections.

A receptacle or device which is either permanently or temporarily connected to the water distribution system of the premises, and demands a supply of water therefrom; or discharges used water, liquid-borne waste materials, or sewage either directly or indirectly to the drainage system.

The water supply pipe between the fixture supply pipe and the water distribution pipe. Also used to refer to a drain from a single fixture to a larger drain pipe.

The drain from the trap of a fixture to the junction of that drain with any other drain pipe. Typically the shortest segment of the drainage system, connecting the fixture trap to the branch drain.

A measure of the probable discharge into the drainage system by various types of plumbing fixtures. The value for a particular fixture depends on its volume rate of drainage discharge, time duration of a single drainage operation, and the average time between successive operations. 1 FU = 28.3 L/min.

The top edge of a receptor or fixture from which water will overflow. Critical reference point for air gap measurements, backflow preventer installation heights, and fixture overflow protection.

A device located at the inlet to the toilet or urinal that supplies a fixed quantity of water for flushing purposes and is actuated by direct water pressure. Also called a flushometer valve.

A drain installed in the floor surface, used to collect water for disposal. Must be provided with a trap and, where subject to backflow from the sewer, a backwater valve. The trap must be kept filled with water (trap seal).

The fall (slope) of a line of pipe in reference to a horizontal plane. In plumbing, grade is expressed as a fraction of pipe diameter per unit of horizontal length, or as a percentage. Minimum grades are specified in Section 309.

A drain branch pipe extending laterally from a soil or waste stack or building drain, with or without vertical sections or offsets, that receives the discharge from one or more fixture drains and conducts it to the soil or waste stack or to the building drain.

Any pipe or fitting that makes an angle of less than 45° with the horizontal plane. A pipe installed at exactly 45° is considered a vertical pipe for code purposes.

See Building Drain. These terms are used interchangeably in older references. The NPC uses "Building Drain" as the primary term.

See Building Trap. A trap installed at the junction of the building drain and building sewer — now generally prohibited by the NPC as individual fixture traps provide equivalent protection.

A waste pipe that does not connect directly with the building drainage system but discharges into the system through an air break or air gap into a trap, fixture, receptor, or interceptor. Used for food equipment, refrigerators, sterilizers — to prevent contamination backflow.

A pipe installed to vent a fixture trap and connecting with the vent system above the fixture served. Provides the most effective protection against siphonage and back-pressure for a single fixture.

Any liquid or liquid-borne waste resulting from the processes employed in industrial, manufacturing, trade, or business establishments. Must meet pretreatment standards before discharge into the public sewer — see Section 304.

A device designed and installed to separate and retain deleterious, hazardous, or undesirable matter from normal wastes and permit normal sewage or liquid wastes to discharge into the disposal terminal by gravity. Examples: grease interceptor, sand/oil interceptor.

The lowest point of the internal cross-section of a pipe or channel. The invert elevation is the elevation of this lowest point, used in drainage calculations and sewer design to determine slope and flow depth.

The exterior drainage pipe for conveying storm water from roof or gutter drains to the building storm drain, combined building drain or sewer, or other means of disposal. Also called a downspout.

A circuit vent that loops back and connects to a stack vent instead of a vent stack. Used where a direct vent stack connection is not practical. The loop must rise continuously from the drain to the vent stack connection.

The principal pipe artery to which branches may be connected. In the water supply system, the main is the pipe from the street or water source to the point where it branches to serve fixtures. In drainage, the building drain is the main drain.

The principal artery of the venting system to which vent branches may be connected. Extends from the building drain upward through the roof. Must be full-size (never reduced) throughout its length.

A fitting or pipe with multiple outlets used to distribute fluids to several branch pipes simultaneously. Common in multi-zone water supply systems and PEX distribution systems.

A numerical designation of size which is a convenient round number approximately equal to a manufacturing dimension of the pipe. Used commercially to identify pipe sizes. Example: 50mm nominal pipe does not have a 50mm inside or outside diameter in all materials.

A combination of elbows or bends that brings one section of the pipe out of line but into a line parallel with the other section. Used to route pipes around structural elements or other obstructions.

The practice, materials, and fixtures used in the installation, maintenance, extension, and alteration of all piping, fixtures, plumbing appliances, and plumbing appurtenances in connection with any of the following: sanitary drainage, storm drainage, water supply, fuel gas piping, and related systems.

Includes the water supply and distribution pipes; plumbing fixtures and traps; soil, waste, and vent pipes; building drains; and building sewers, including their respective connections, devices, and appurtenances within the property lines of the premises.

Water free from impurities present in amounts sufficient to cause disease or harmful physiological effects, and conforming in its bacteriological and chemical quality to the requirements of the Philippine National Standards for Drinking Water (PNSDW).

The force per unit area exerted by a liquid or gas. In plumbing: static pressure is pressure with no flow; residual pressure is pressure during flow; working pressure is the maximum operating pressure a system component is designed for.

A self-operated valve that reduces the upstream water pressure to a safe, pre-set downstream pressure. Required where supply pressure exceeds 550 kPa (80 psi) to protect fixtures and appliances.

A cylindrical conduit or conductor, the wall thickness of which is standardized. Designated by its nominal diameter. For pipe sizing and wall thickness standards, refer to Section 314 and applicable ASTM or PNS standards.

Installed receptacles, devices, or appliances which are supplied with water or which receive or retain liquids or liquid-borne wastes and discharge such liquids or liquid-borne wastes, either directly or indirectly, to the drainage system. See Chapter 4 for fixture requirements.

A pipe whose primary function is to provide circulation of air between drainage and vent systems. Installed in drainage systems with long horizontal branch drains to prevent pressure imbalances that could cause trap siphonage.

An unobstructed open edge of a fixture. The flood-level rim is the top edge from which overflow would occur. Used to set minimum height of vacuum breakers and air gaps.

A water supply pipe which proceeds vertically upward from a branch or main to the fixtures it serves. In tall buildings, water risers are sized for velocity and pressure loss — typically not exceeding 3.0 m/s velocity.

The installation of all parts of the plumbing system which can be completed prior to the installation of fixtures. This includes all drain, water supply, and vent piping, and the necessary fixture supports. Rough-in dimensions are manufacturer-specific for each fixture type.

A sewer that carries sewage and excludes storm, surface, and ground water. Distinguished from storm sewer and combined sewer. In areas with separate sewer systems, storm water and sewage must not be mixed — see Section 308.

A watertight receptacle which receives the discharge of a drainage system or part thereof, and is designed and constructed so as to separate solids from the liquid, digest organic matter through a period of detention, and allow the liquids to discharge into the soil outside of the tank through a system of open-joint or perforated piping. See Chapter 10.

Any liquid waste containing animal or vegetable matter in suspension or solution, and may include liquids containing chemicals in solution.

Any pipe which conveys the discharge of water closets or fixtures having similar functions, with or without the discharge from other fixtures. Carries fecal matter and must be sized appropriately — minimum 100mm (4 in) nominal diameter for any WC connection.

The generic term for any vertical line of soil, waste, or vent piping extending through one or more stories. A soil stack carries WC discharge. A waste stack carries only non-WC fixture waste. A vent stack carries only air.

The extension of a soil or waste stack above the highest horizontal drain connected to the stack. Terminates through the roof to atmosphere. Must not be reduced in size from the stack below.

A fitting or device so designed and constructed as to provide, when properly vented, a liquid seal which will prevent the passage of air and gases through it without materially affecting the flow of sewage or waste water through it. Every fixture connected to the drainage system must have a trap.

That portion of a fixture drain between a trap and its vent. The length of the trap arm is limited to prevent self-siphonage — maximum developed length is specified in Chapter 8 based on pipe diameter.

The maximum vertical depth of liquid that a trap will retain. A trapped fixture maintains a water plug in the trap that blocks sewer gases from entering the building. Minimum depth: 50 mm. Maximum depth: 100 mm. Deeper is not necessarily better — it can slow draining.

A conduit for conveying fluids, generally distinguished from pipe by the method of size designation and, often, by its wall thickness. Copper tube (Types K, L, M) and PEX tubing are specified by outside diameter; pipe by nominal bore.

The point in a P-trap or S-trap at which the water surface is maintained. Defines the upper level of the trap seal water. The vertical distance from the trap weir down to the dip (lowest point of the U) is the trap seal depth.

A device that prevents back-siphonage by admitting air into a pipe system when the pressure in that line becomes less than atmospheric. Two main types: pressure vacuum breaker (PVB) and atmospheric vacuum breaker (AVB). Must be installed above flood level rim.

Any pipe provided to ventilate a building drainage system and to prevent trap siphonage and back-pressure. Carries only air (dry vent) or air plus a small volume of liquid (wet vent). Must terminate to atmosphere — through roof or to a relief vent.

A vertical vent pipe installed primarily for the purpose of providing circulation of air to and from any part of the building drainage system. Connects to the building drain at the bottom and extends through the roof at the top. Must not be offset below the highest connected branch.

A pipe or pipes installed to provide a flow of air to or from a drainage system or to provide a circulation of air within such system to protect trap seals from siphonage and back-pressure.

A pipe that conveys only liquid waste, free of fecal matter. Distinguished from a soil pipe which carries WC discharge. Waste pipes typically carry discharge from lavatories, sinks, bathtubs, showers, and laundry fixtures.

A fixture that consists of a water-flushed bowl with a seat, used for the disposal of human excrement. Requires a minimum 100mm (4 in) soil pipe connection. Must be supplied with potable water only and have a trap integral with the bowl.

The water service pipe, the water distributing pipes, and the necessary connecting pipes, fittings, control valves, and all appurtenances in or adjacent to the building or premises. Does not include the public water main or the water meter.

A pipe that serves simultaneously as a drain for one fixture and as a vent for one or more other fixtures. Limited to fixtures connected to the same horizontal branch. The wet-vented section must be sized to handle both drainage and venting functions — typically one pipe size larger than the drain alone would require.

A pipe connecting upward from a soil or waste stack to a vent stack for the purpose of preventing pressure changes in the stacks. Installed at every fifth branch interval counting from the top in tall buildings. Required in buildings over 10 storeys.