Household Waste
Drainage Systems
When we flush a toilet, empty a bath tub or sink, wash clothes,
etc. we run water and waste through a system of pipes in our
homes out to a waste system of some sort (we’ll look at this a
little later).
Drain pipes in our homes/buildings have to be the correct size. If
they are too small they won’t permit waste to flow and if they are
too large it becomes a problem when trying to install them and it
doesn’t carry away the waste correctly.
From our sinks, toilets, etc. the waste runs into pipes.
These pipes have to be at the correct angle in order for
the waste and water to flow together. If it is too steep the
water will leave the waste behind. If too low neither will
run correctly. This will cause major problems in the
The water and waste then move to a larger pipe called
the soil stack. This pipe connects all the pipes and leads
to the main pipe going from the building to the outside
waste system.
Inside the pipe system of the building there needs to
be vents strategically placed. These vents allow air
into the system so that the pipes can run correctly
and also to vent the gases that build up from the
septic waste. If these gases aren’t vented correctly
they not only cause a bad odor but can be potential
fatal or cause explosions.
Problems with vents
A plugged vent can trap dangerous gases and inhibits
drainage; similar to plugging a drinking straw with
your thumb to hold liquid.
Make sure the vent doesn't terminate in the attic.
Trapped sewer gases can be dangerous, stink and
cause serious structural problems. A system without a
vent may actually suck water out of a sink's trap, or do
the reverse and fill the sink with water when another
fixture drains.
A trap blocks sewer/septic gases. Without one, sewer
gases can flow up the stack, drain pipes and come out
wherever there's a drain. A trap looks like a "U" and is
installed below the drain.
When water drains, the trap's
shape causes a small amount of
water to remain in the bend. That
water blocks any gases from
moving up the pipe and entering
the room.
NOTE: Traps are needed on all drains. That is, sinks,
tubs, showers, washers, floor drains all need to have a
trap in their drain lines. In most cases, a toilet has a
built-in trap and doesn't require a trap in the drain line
In the pipeline there needs to be installed special areas:
Cleanouts are put at different spots to allow access to the pipes if there is a
blockage. These are Tees or Wyes placed in the system.
Backwater valves are placed in the system as well. These valves do not let
waste and water back into the system once it leaves the house/building.
This has a one way flap the allows things to flow only one way.
Backwater Valve
Waste Systems
Once outside the home/building there are
two main ways we get rid of human waste
and water. Depending on where you live
you will use one of these systems
1. Municipal waste systems
2. Septic Systems
Municipal Waste systems
The overall state of Canada’s water quality is relatively
high, but is increasingly being threatened by
contaminants from waste systems near populated areas
and industrial development.
National Pollutant Release Inventory
Domestic wastewater includes typical wastes from the
kitchen, bathroom, and laundry, as well as any other
wastes that people may accidentally or intentionally pour
down the drain.
Many of the waste systems around our province dump the waste
directly into the ocean. There are a series of pipes which come
from houses, businesses, industry, etc. That feed into a much
larger sewer trunk. These underground pipes then feed to a main
area and all the waste water and run off water is dumped into
different locations.
Most of the waste water in the St. John’s Metro region goes
directly into St. John’s harbour. The region is currently building
a new sewage treatment plant so that all contaminants can be
removed from the waste system prior to the water going to the
Treatment plant
Private Treatment: The Septic Tank
In rural areas where houses are spaced so
far apart that a sewer system would be too
expensive to install, people install their
own, private sewage treatment plants.
These are called septic tanks.
A septic tank is simply a big concrete,
plastic or steel tank that is buried in the
yard. Wastewater flows into the tank at
one end and leaves the tank at the other.
Anything that floats rises to the top and forms a layer
known as the scum layer. Anything heavier than
water sinks to form the sludge layer. In the middle is a
fairly clear water layer. This body of water contains
bacteria and chemicals like nitrogen and
phosphorous that act as fertilizers, but it is largely
free of solids.
As new water enters the tank, it displaces the water that's
already there. This water flows out of the septic tank and into a
drain field. A drain field is made of perforated pipes buried in
trenches filled with gravel.
A septic system is normally powered by nothing but gravity.
Water flows down from the house to the tank, and down from
the tank to the drain field. It is a completely passive system.
There are precautions to be taken with any waste and water system. This
is especially true for a well and septic system.
When planning your system you need to ensure that your septic system is
far enough away from your well so that the run off from the septic field
does not interfere with the well. This can have a deadly affect.
Activity:Using the book Modern Plumbing by Keith
Blankenbaker complete the following:
Explain the various venting methods. P. 287
Why is selecting the right size pipe important in a
DWV system? P.281
What are two main things that must be considered
when designing a plumbing system? P.295
What is the difference between a Sanitary Tee and a
Vent Tee? P.222
What is the difference between a Wye and a TY? P.222
A great resource for the description of the household plumbing system can be
found at:

Waste System