Plumbing may be defined as practice, materials, and fixtures
used in the installation, maintenance, and alteration of all
piping, fixtures, appliances, and appurtenances in connection
with sanitary or storm drainage facilities, the venting system,
and the public or private water supply systems. Plumbing does
not include the trade of drilling water wells, installing water
softening equipment, or the business of manufacturing or selling
plumbing fixtures, appliances, equipment, or hardware. A
plumbing system consists of three separate parts: an adequate
potable water supply system, a safe, adequate drainage system
and ample fixtures and equipment.
The generalized inspection of a home is concerned with a safe
water supply system, an adequate drainage system, and ample and
proper fixtures and equipment. This explains features of a
residential plumbing system and the basic plumbing terms the
inspector must know and understand to identify properly housing
code violations involving plumbing and the more complicated
defects that he will refer to the appropriate agencies.
Pressure absorbing devices that eliminate water hammer. They
should be installed as close as possible to the valves or faucet
and at the end of long runs of pipe.
Air Gap (Drainage System)
The unobstructed vertical distance through the free atmosphere
between the outlet of a water pipe and the flood level rim of
the receptacle into which it is discharging.
Air Gap (Water Distribution System)
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.
An air lock is a bubble of air which restricts the flow of water
in a pipe.
The flow of water or other liquids, mixtures, or substances into
the distributing pipes of a potable water supply from any source
or sources other than the intended source. Back siphonage is one
type of backflow.
The flowing back of used, contaminated, or polluted water from a
plumbing fixture or vessel into a potable water supply due to a
negative pressure in the pipe.
Any part of the piping system other than the main, riser, or
A vent connecting one or more individual vents
with a vent stack.
The part of the lowest piping of a drainage system that receives
the discharge from soil, waste, or other drainage pipes inside
the walls of the building (house) and conveys it to the building
sewer beginning 3 feet outside the building wall.
Any physical connection or arrangement between two otherwise
separate piping systems, one of which contains potable water and
the other either water of unknown or questionable safety or
steam, gas, or chemical whereby there may be a flow from one
system to the other, the direction of flow depending on the
pressure differential between the two systems. (See Backflow and
An area containing a series of one or more trenches lined with
coarse aggregate and conveying the effluent from the septic tank
through vitrified clay Pine or perforated, non-metallic pipe,
laid in such a manner that the flow will be distributed with
reasonable uniformity into natural soil.
Any pipe that carries waste water or water-borne waste in a
building (house) drainage system.
Flood Level Rim
The top edge of a receptacle from which water
A device that discharges a predetermined quantity of water to
fixtures for flushing purposes and is closed by direct water
A device located at the bottom of the tank for flushing water
closets and similar fixtures.
Potable water that is heated to at least 120F and used for
cooking, cleaning, washing dishes, and bathing.
Contrary to sanitary principles injurious to health.
A device designed and installed so as to separate and retain
deleterious, hazardous, or undesirable matter from normal wastes
and permit normal sewage or liquid wastes to discharge into the
drainage system by gravity.
An exterior drainage pipe for conveying storm water from roof or
gutter drains to the building storm drain, combined building
sewer, or other means of disposal.
The principal artery of the venting system, to which vent
branches may be connected.
See Public Sewer.
The word pertains to devices making use of compressed air as in
pressure tanks boosted by pumps.
Water having no 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 Public Health Service drinking water standards or meeting
the regulations of the public health authority having
P & T (Pressure and Temperature) Relief Valve
A safety valve installed on a hot water storage tank to limit
temperature and pressure of the water.
A trap with a vertical inlet and a horizontal outlet.
A common sewer directly controlled by public authority.
An auxiliary vent that permits additional circulation of air in
or between drainage and vent systems.
A watertight receptacle that receives the discharge of a
building's sanitary drain system or part thereof and is designed
and constructed so as to separate solid 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, or through a seepage
A sewerage system comprises all piping,
appurtenances, and treatment facilities used for the collection
and disposal of sewage, except plumbing inside and in connection
with buildings served and the building drain.
The pipe that directs the sewage of a house to the receiving
sewer, building drain, or building sewer.
The vertical piping that terminates in a roof vent and carries
off the vapors of a plumbing system.
An extension of a solid or waste stack above the highest
horizontal drain connected to the stack. Sometimes called a
waste vent or a soil vent.
A sewer used for conveying rain water, surface water,
condensate. cooling water, or similar liquid waste.
A trap is a fitting or device that provides a liquid seal to
prevent the emission of sewer gases without materially affecting
the flow of sewage or waste water through it.
A device to prevent backflow (back siphonage) by means of an
opening through which air may be drawn to relieve negative
The vertical vent pipe installed to provide air circulation to
and from the drainage system and that extends through one or
The loud thump of water in a pipe when a valve or faucet is
Water Service Pipe
The pipe from the water main or other sources of potable water
supply to the water-distributing system of the building served.
Water Supply System
The water supply system consists of the water service pipe, the
water-distributing pipes, the necessary connecting pipes,
fittings, control valves, and all appurtenances in or adjacent
to the building or premises.
A vent that receives the discharge of waste other than from
A pipe connecting upward from a soil or waste stack to a vent
stack for the purpose of preventing pressure changes in the
Main Features of an Indoor Plumbing System
The primary functions of the plumbing system within the house
are as follows:
1. To bring an adequate and potable supply of hot and cold water
to the users of the dwelling.
2. To drain all waste water and sewage discharged from these
fixtures into the public sewer, or private disposal system.
It is, therefore, very important that the housing inspector
familiarize himself fully with all elements of these systems so
that he may recognize inadequacies of the structure's plumbing
as well as other code violations.
Elements of a Plumbing System
The piping of a house service line should be as short as
possible. Elbows and bends should be kept to a minimum since
these reduce the pressure and therefore the supply of water to
fixtures in the house. The house service line should also be
protected from freezing. The burying of the line under 4 feet of
soil is a commonly accepted depth to prevent freezing. This
depth varies, however, across the country from north to south.
The local or state plumbing code should be consulted for the
recommended depth in your area of the country.
The materials used for a house service may be copper, cast iron,
steel or wrought iron. The connections used should be compatible
with the type of pipe used.
Corporation stop - The corporation stop is connected to the
water main. This connection is usually made of brass and can be
connected to the main by use of a special tool without shutting
off the municipal supply. The valve incorporated in the
corporation stop permits the pressure to be maintained in the
main while the service to the building is completed.
Curb stop - The curb stop is a similar valve used to isolate the
building from the main for repairs, nonpayment of water bills,
or flooded basements. Since the corporation stop is usually
under the street and would necessitate breaking the pavement to
reach the valve, the curb stop is used as the isolation valve.
Curb stop box - The curb stop box is an access box to the curb
stop for opening and closing the valve. A long-handled wrench is
used to reach the valve.
Meter stop -The meter stop is a valve placed on
the street side of the water meter to isolate the meter for
installation or maintenance. Many codes require a gate valve on
the house side of the meter to shut off water for house plumbing
repairs. The curb and meter stops are not to be used frequently
and can be ruined in a short time if used very frequently.
Water meter - The water meter is a device used to measure the
amount of water used in the house. It is usually the property of
the city and is a very delicate instrument that should not be
abused. Since the electric system is usually grounded to the
water line, a grounding loop-device should be installed around
the meter. Many meters come with a yoke that maintains
electrical continuity even though the meter is removed.
Hot and Cold Water Main Lines: The hot and cold water main lines
are usually hung from the basement ceiling and are attached to
the water meter and hot-water tank on one side and the fixture
supply risers on the other. These pipes should be installed in a
neat manner and should be supported by pipe hangers or straps of
sufficient strength and number to prevent sagging. Hot and cold
water lines should be approximately 6 inches apart unless the
hot water line is insulated. This is to insure that the cold
water line does not pick up heat from the hot water line. The
supply mains should have a drain valve or stop and waste valve
in order to remove water from the system for repairs. These
valves should be on the low end of the line or on the end of
each fixture riser.
The fixture risers start at the basement main and
rise vertically to the fixtures on the upper floors. In a
one-family dwelling, riser branches will usually proceed from
the main riser to each fixture grouping. In any event the
fixture risers should not depend on the branch risers for
support but should be supported with a pipe bracket. Each
fixture is then connected to the branch riser by a separate
line. The last fixture on a line is usually connected directly
to the branch riser. ( See bottom of page for Pex Piping )
Hot Water Heaters: Hot water heaters are usually powered by
electricity, fuel oil, gas, or in rare cases, coal or wood. They
consist of a space for heating the water and a storage tank for
providing hot water over a limited period of time. All hot water
heaters should be fitted with a temperature-pressure relief
valve no matter what fuel is used. This valve will operate when
either the temperature or the pressure becomes too high due to
an interruption of the water supply or a faulty thermostat.
Pipe Sizes: The size of basement mains and risers depends on the
number of fixtures supplied. However, a 3/4 inch pipe is usually
the minimum size used. This allows for deposits on the pipe due
to hardness in the water and will usually give satisfactory
volume and pressure.
The water supply brought into the house and used is discharged
through the drainage system. This system is either a sanitary
drainage system carrying just interior waste water or a combined
system carrying interior waste and roof runoff.
Sanitary Drainage System: The proper sizing of
the sanitary drain or house drain depends on the number of
fixtures it serves. The usual minimum size is 6 inches in dial
diameter. The materials used are usually cast iron, vitrified
clay, plastic, and in rare cases, lead. For proper flow in the
drain the pipe should be sized so that it flows approximately
one-half full. This ensures proper scouring action so that the
solids contained in the waste will not be deposited in the pipe.
Sizing of house drain - The Uniform Plumbing Code Committee has
developed a method of sizing of house drains in terms of
"fixture units." One ''fixture unit" equals approximately 71 D2
gallons of water per minute. This is the surge flow-rate of
water discharged from a wash basin in 1 minute. All other
fixtures have been related to this unit.
Sanitary Drain Sizes
Grade of house drain - A house drain or building sewer should be
sloped toward the sewer to ensure scouring of the drain. The
usual pitch of a house or building sewer is 1 D4 inch fall in 1
foot of length.
Fixture and branch drains - A branch drain is a waste pipe that
collects the waste from two or more fixtures and conveys it to
the building or house sewer. It is sized in the same way as the
house sewer, taking into account that all water closets must
have a minimum 3-inch diameter drain, and only two water closets
may connect into one 3-inch drain.
All branch drains must join the house drain with
a "Y" -type fitting. The same is true for fixture drains joining
branch drains. The "Y" fitting is used to eliminate, as much as
possible, the deposit of solids in or near the connection. A
build-up of these solids will cause a blockage in the drain.
Traps - A plumbing trap is a device used in a waste system to
prevent the passage of sewer gas into the structure and yet not
hinder the fixture's discharge to any great extent. All fixtures
connected to a household plumbing system should have a trap
installed in the line.
The effect of sewer gases on the human body are known; many are
extremely harmful. Additionally, certain sewer gases are
explosive. A trap will prevent these gases from passing into the
structure. The depth of the seal in a trap is usually 2 inches.
A deep seal trap has a 4-inch seal.
The purpose of a trap is to seal out sewer gases from the
structure. Since a plumbing system is subject to wide variations
in flow, and this flow originates in many different sections of
the system, there is a wide variation in pressures in the waste
lines. These pressure differences tend to destroy the water seal
in the trap. To counteract this problem mechanical traps were
introduced. It has been found, however, that the corrosive
liquids flowing in the system corrode or jam these mechanical
traps. It is for this reason that most plumbing codes prohibit
There are many manufacturers of traps, and all have varied the
design somewhat. The "P" trap is usually found in lavatories,
sinks, urinals, drinking fountains, showers, and other
installations that do not discharge a great deal of water.
The drum trap is another water seal-type trap. They are usually
used in the 4x5-inch or 4x8-inch sizes. These traps have a
greater sealing capacity than the "P" trap and pass large
amounts of water quickly. Drum traps are commonly connected to
bathtubs, foot baths, sitz baths, and modified shower baths.
The "S" 1 and the 3h "S" trap should not be us in plumbing
installations. They are almost impossible to ventilate properly,
and the 3h "S" trap forms a perfect siphon.
The bag trap, an extreme form of "S" trap, is seldom found.
Any trap that depends on a moving part for its effectiveness is
usually inadequate and has been prohibited by the local plumbing
codes. These traps work, but their design usually results in
their being higher priced than the "P" or drum traps. It should
be remembered that traps are used only to prevent the escape of
sewer gas into the structure. They do not compensate for
pressure variations. Only proper venting will eliminate pressure
A plumbing system is ventilated to prevent trap seal loss,
material deterioration. and flow retardation.
Trap seal loss
The seal in a plumbing trap may be lost due to siphonage (direct
and indirect or momentum), back pressure, evaporation, capillary
attraction, or wind effect. The first two named are probably the
most common causes of loss. If a waste pipe is placed vertically
after the fixture trap, as in an "S" trap, the waste water
continues to flow after the fixture is emptied and clears the
trap. This is caused by the pressure of air on the fixture
water's being greater than the pressure of air in the waste
pipe. The action of the water discharging into the waste pipe
removes the air from that pipe and thereby causes a negative
pressure in the waste line. In the case of indirect or momentum
siphonage, the flow of water past the entrance to a fixture
drain in the waste pipe removes air from the fixture drain. This
reduces the air pressure in the fixture drain, and the entire
assembly acts as an aspirator such as the physician uses to
spray an infected throat.
The flow of water in a soil pipe varies according to the
fixtures being used. A lavatory gives a small flow and a water
closet a large flow. Small flows tend to cling to the sides of
the pipe, but large ones form a slug of waste as they drop. As
this slug of water falls down the pipe the air in front of it
becomes pressurized. As the pressure builds it seeks an escape
point. This point is either a vent or a fixture outlet. If the
vent is plugged or there is no vent, the only escape for this
air is the fixture outlet. The air pressure forces the trap seal
up the pipe into the fixture. If the pressure is great enough
the seal is blown out of the fixture entirely. Figures 6-17 and
6-18 illustrate this type of problem.
Vent pipe installation is similar to that of soil and waste
pipe. The same fixture unit criteria are used. Vent pipes of
less than 11 D4 inches in diameter should not be used. Vents
smaller than this diameter tend to clog and do not perform their
Individual fixture ventilation - This type of ventilation is
generally used for sinks, lavatories, drinking fountains, and so
Unit venting - The unit venting system is commonly used in
apartment buildings. This type of system saves a great deal of
money and space when fixtures are placed back to back in
Wet venting - Wet venting of a plumbing system is
common in household bathroom fixture grouping. It is exactly
what the name implies: the vent pipe is used as a waste line.
Total drainage system
Up to now we have talked about the drain, soil waste, and vent
systems of a plumbing system separately. For a working system,
however, they must all be connected.
This is the newest material to come on the market
in response to the problems with Poly. It is expensive but good.
Unlike PVC, it can be used for hot water lines. I see it in the
home improvement places. I have used CPVC frequently in the
past. PEX is especially valued in parts of the country where
water lines frequently freeze for its ability to stretch without
splitting. PEX is increasingly available in the chain home
improvement stores. They may have a few pre-cut pieces and
connectors, but will not have what you need for a plumbing
project on your mobile home. You will need to visit a mobile
home supply store to get the assortment needed for completing a