# QUESTION ANSWER
1 What does DWV stand for in DWV stands for Drain, Waste, and
plumbing? Vent. It refers to the system of
pipes that carries wastewater and
sewage away from fixtures and
vents gases to the atmosphere.
2 What is the primary purpose The primary purpose is to remove
of a DWV system? wastewater and sewage from
building fixtures efficiently and
safely, while also providing air
circulation to prevent siphoning of
trap seals and venting sewer gases
outdoors.
3 What is the difference Drain pipes carry water from
between a drain pipe and a fixtures (like floor drains) that may
waste pipe? not carry solid waste, while waste
pipes carry water and solid waste
from fixtures such as toilets, sinks,
and dishwashers.
DWV Design – 300 Q&A Reference Guide | Page 1
,# QUESTION ANSWER
4 What is a soil pipe? A soil pipe is a pipe that conveys
sewage containing fecal matter
from toilets or urinals to the sewer
or septic system. It is typically
larger in diameter than waste
pipes.
5 What is the function of a vent Vent pipes allow air into the
pipe in a DWV system? drainage system to maintain
atmospheric pressure, preventing
siphoning of trap water seals,
eliminating odors, and allowing
wastewater to flow freely.
6 What materials are Common materials include PVC
commonly used for DWV (polyvinyl chloride), ABS
piping? (acrylonitrile butadiene styrene),
cast iron, copper, and galvanized
steel. PVC and ABS are most
common in modern residential
construction.
7 What is the minimum slope The minimum slope for horizontal
required for horizontal drain drain pipes is typically 1/4 inch per
pipes? foot (2%) for pipes up to 3 inches in
diameter. Pipes 4 inches and larger
may use 1/8 inch per foot (1%).
8 What is a building drain? The building drain is the lowest
horizontal pipe in the DWV system
that receives discharge from all
DWV Design – 300 Q&A Reference Guide | Page 2
, # QUESTION ANSWER
other drainage pipes within the
building and carries it to the
building sewer.
9 What is a building sewer? The building sewer is the pipe
extending from the building drain to
the public sewer main, private
sewer, or septic system. It begins
2–5 feet outside the building
foundation.
10 What is a stack in DWV A stack is a vertical pipe in the
terminology? drainage system. A soil stack
receives discharge from toilets; a
waste stack receives discharge
from sinks, tubs, and other non-
toilet fixtures; a vent stack provides
ventilation.
2. Traps & Trap Seals
# QUESTION ANSWER
11 What is a plumbing trap and A plumbing trap is a curved section
why is it required? of pipe that retains a small amount
of water, creating a water seal that
prevents sewer gases from
DWV Design – 300 Q&A Reference Guide | Page 3
, # QUESTION ANSWER
entering the building through fixture
drain openings.
12 What is the required water The required water seal depth for
seal depth for most traps? most plumbing traps is a minimum
of 2 inches and a maximum of 4
inches, as specified in most
plumbing codes.
13 What is a P-trap? A P-trap is the most common type
of fixture trap, shaped like the letter
'P' on its side. It is used under
sinks, lavatories, and other fixtures
and is connected to the drain and
waste pipe.
14 What is an S-trap and why is An S-trap is shaped like the letter
it generally prohibited? 'S' and is generally prohibited
because it is prone to self-
siphoning, which removes the
water seal and allows sewer gas to
enter the building.
15 What is a drum trap? A drum trap is a cylindrical trap
with a removable cover, historically
used for bathtubs. Most codes now
prohibit new installations due to
poor self-cleaning properties and
difficulty inspecting.
DWV Design – 300 Q&A Reference Guide | Page 4
1 What does DWV stand for in DWV stands for Drain, Waste, and
plumbing? Vent. It refers to the system of
pipes that carries wastewater and
sewage away from fixtures and
vents gases to the atmosphere.
2 What is the primary purpose The primary purpose is to remove
of a DWV system? wastewater and sewage from
building fixtures efficiently and
safely, while also providing air
circulation to prevent siphoning of
trap seals and venting sewer gases
outdoors.
3 What is the difference Drain pipes carry water from
between a drain pipe and a fixtures (like floor drains) that may
waste pipe? not carry solid waste, while waste
pipes carry water and solid waste
from fixtures such as toilets, sinks,
and dishwashers.
DWV Design – 300 Q&A Reference Guide | Page 1
,# QUESTION ANSWER
4 What is a soil pipe? A soil pipe is a pipe that conveys
sewage containing fecal matter
from toilets or urinals to the sewer
or septic system. It is typically
larger in diameter than waste
pipes.
5 What is the function of a vent Vent pipes allow air into the
pipe in a DWV system? drainage system to maintain
atmospheric pressure, preventing
siphoning of trap water seals,
eliminating odors, and allowing
wastewater to flow freely.
6 What materials are Common materials include PVC
commonly used for DWV (polyvinyl chloride), ABS
piping? (acrylonitrile butadiene styrene),
cast iron, copper, and galvanized
steel. PVC and ABS are most
common in modern residential
construction.
7 What is the minimum slope The minimum slope for horizontal
required for horizontal drain drain pipes is typically 1/4 inch per
pipes? foot (2%) for pipes up to 3 inches in
diameter. Pipes 4 inches and larger
may use 1/8 inch per foot (1%).
8 What is a building drain? The building drain is the lowest
horizontal pipe in the DWV system
that receives discharge from all
DWV Design – 300 Q&A Reference Guide | Page 2
, # QUESTION ANSWER
other drainage pipes within the
building and carries it to the
building sewer.
9 What is a building sewer? The building sewer is the pipe
extending from the building drain to
the public sewer main, private
sewer, or septic system. It begins
2–5 feet outside the building
foundation.
10 What is a stack in DWV A stack is a vertical pipe in the
terminology? drainage system. A soil stack
receives discharge from toilets; a
waste stack receives discharge
from sinks, tubs, and other non-
toilet fixtures; a vent stack provides
ventilation.
2. Traps & Trap Seals
# QUESTION ANSWER
11 What is a plumbing trap and A plumbing trap is a curved section
why is it required? of pipe that retains a small amount
of water, creating a water seal that
prevents sewer gases from
DWV Design – 300 Q&A Reference Guide | Page 3
, # QUESTION ANSWER
entering the building through fixture
drain openings.
12 What is the required water The required water seal depth for
seal depth for most traps? most plumbing traps is a minimum
of 2 inches and a maximum of 4
inches, as specified in most
plumbing codes.
13 What is a P-trap? A P-trap is the most common type
of fixture trap, shaped like the letter
'P' on its side. It is used under
sinks, lavatories, and other fixtures
and is connected to the drain and
waste pipe.
14 What is an S-trap and why is An S-trap is shaped like the letter
it generally prohibited? 'S' and is generally prohibited
because it is prone to self-
siphoning, which removes the
water seal and allows sewer gas to
enter the building.
15 What is a drum trap? A drum trap is a cylindrical trap
with a removable cover, historically
used for bathtubs. Most codes now
prohibit new installations due to
poor self-cleaning properties and
difficulty inspecting.
DWV Design – 300 Q&A Reference Guide | Page 4
