Upon completing this chapter, you will be able to:
Identify the scope and intent of the IPC chapter governing sanitary drainage.
Distinguish between building drains, building sewers, and sanitary drains.
Apply minimum slope requirements for various pipe sizes.
Recognize prohibited connections and installations.
Calculate and apply the fixture unit loading method for sizing drainage piping.
Understand the requirements for cleanouts, offsets, and sumps.
Navigate the IPC efficiently to locate drainage code sections during the open-book exam.
1.1 Scope and General Principles
The sanitary drainage system is the network of piping that carries sewage and liquid waste from fixtures to the public sewer or private disposal system. The IPC establishes minimum standards to protect health, prevent structural damage, and ensure the safe conveyance of waste.
Key definitions you must know:
Building drain: The lowest piping that receives discharge from soil, waste, or other drainage pipes inside the walls of a building and conveys it to the building sewer, beginning 3 feet (914 mm) outside the building wall.
Building sewer: The piping that extends from the building drain to the public sewer or private disposal system.
Soil pipe: A pipe that conveys sewage containing fecal matter.
Waste pipe: A pipe that conveys liquid waste free of fecal matter.
Sanitary drain: A pipe that carries sewage or waste water exclusively.
The code applies to all piping, fittings, and appurtenances from the point of fixture connection to the point of disposal. It does not govern storm drainage, which is covered separately in the IPC.
1.2 Prohibited Installations and Connections
The IPC is strict about what cannot be done. Memorize these prohibitions for quick recall:
No cross-connection: Sanitary drainage must never be connected to a storm drain, storm sewer, or roof drain system.
No indirect connection: A sanitary drain cannot be directly connected to a waste receptor that receives discharge from an indirect waste pipe unless a trap and air gap are provided.
No food waste disposers may discharge into a grease interceptor unless specifically designed for that purpose.
No drainage pipe may be installed in an elevator shaft, air duct, or plenum.
No piping conveying corrosive or toxic waste may be installed without approved materials and neutralization treatment.
No trap may be installed on a combination fixture unless the fixture is designed for it.
No fixture may be double-trapped (two traps in series on the same fixture drain).
Inspector’s eye: On site, inspectors verify that no roof or storm water lines are tied into the sanitary system. They also check that no drainage pipe is embedded in a concrete slab without prior approval and proper protection.
1.3 Slope Requirements
Gravity drainage requires a minimum slope to ensure self-scouring velocity. The code sets minimum slopes based on pipe diameter. These are minimum values; you may use steeper slopes, but never shallower.
Pipe Diameter (inches)
Minimum Slope (inch per foot)
2.5 or less
1/4 (0.25)
3
1/4 (0.25)
4
1/8 (0.125)
5
1/8 (0.125)
6
1/8 (0.125)
8 or larger
1/16 (0.0625)
Critical note: For pipe sizes 4 inches and larger, the slope may be reduced to 1/16 inch per foot if the pipe is sized for a flow of at least 7 feet per second (2.1 m/s) at one-third full. This is an engineering exception, not a field default.
Inspector’s eye: Inspectors use a level and a tape measure to check slope on exposed piping. They also verify that the slope is uniform; a pipe that sags or has a belly will collect solids and cause blockages.
1.4 Sizing of Sanitary Drainage Systems
Sizing is based on drainage fixture unit (dfu) values. The IPC provides tables that assign a dfu value to each type of fixture. The total dfu load on a pipe determines its minimum required diameter.
Key dfu values you should recall (from IPC Table 709.1):
Water closet (toilet), private: 3 dfu
Water closet, public: 6 dfu
Bathtub or shower: 2 dfu
Lavatory (sink): 1 dfu
Kitchen sink (domestic): 2 dfu
Dishwasher (domestic): 2 dfu
Washing machine (domestic): 3 dfu
Floor drain: 2 dfu
Sink (service or mop): 3 dfu
Sizing method:
54.Determine the total dfu load for each branch or stack.
55.Use the appropriate sizing table (IPC Table 710.1 for horizontal branches, Table 710.1(1) for stacks) to find the minimum pipe diameter.
56.For a building drain, sum all dfu loads and use the table for horizontal drains.
Example: A horizontal branch serving two private water closets (3 + 3 = 6 dfu) and one lavatory (1 dfu) totals 7 dfu. According to the table, a 3-inch pipe is required (the minimum for any pipe carrying water closet discharge is 3 inches).
Building drain (minimum): 4 inches if it serves a water closet
Inspector’s eye: Inspectors verify that no pipe smaller than 3 inches carries water closet discharge. They also check that the dfu load on a pipe does not exceed the table’s capacity for the installed diameter.
1.5 Cleanouts
Cleanouts are required to allow access for clearing blockages. The IPC specifies their location, size, and spacing.
Required locations:
At the upper end of every horizontal branch (the base of each vertical stack).
At every change of direction greater than 45 degrees (a 90-degree turn requires a cleanout at the change).
At intervals of no more than 100 feet (30,480 mm) on horizontal runs.
At the base of each vertical stack (a cleanout at the bottom of the stack).
At the connection of the building drain to the building sewer (outside, near the wall).
Size requirements:
Cleanout size must be equal to the pipe size up to 4 inches.
For pipes larger than 4 inches, the cleanout may be 4 inches.
Access: Cleanouts must be accessible. They cannot be concealed without an access panel. The clearance in front of a cleanout must be at least 18 inches (457 mm) to allow rodding.
Inspector’s eye: Inspectors look for cleanouts at the base of stacks and at changes in direction. A common deficiency is a 90-degree elbow without a cleanout on a long horizontal run.
1.6 Offsets and Changes in Direction
The IPC limits the use of certain fittings to prevent flow restriction and clogging.
Horizontal to vertical: Use a wye or a combination wye-eighth bend (wye + 45-degree elbow). A sanitary tee is not permitted for this transition.
Vertical to horizontal: Use a wye or a combination wye-eighth bend. A short-radius quarter bend is prohibited.
Horizontal to horizontal: Use a wye or a combination wye-eighth bend. A sanitary tee is not allowed.
Changes in direction: The total change in direction in a drainage system shall not exceed 135 degrees between cleanouts. This means you cannot have two 90-degree turns without a cleanout between them.
Fittings you may NOT use for drainage:
Short-radius quarter bends (for change from vertical to horizontal)
Sanitary tees used in a horizontal run
Bushings that reduce the diameter of a pipe at a fitting (must use a proper reducer)
Inspector’s eye: Inspectors check that all horizontal-to-vertical transitions use a wye pattern. They also verify that no fitting creates a sharp turn that would impede flow.
1.7 Sumps and Ejectors
When fixtures are located below the elevation of the public sewer or septic system, drainage cannot flow by gravity. In such cases, a sump and ejector pump are required.
Requirements:
The sump must be vented (connected to a vent stack).
The ejector discharge pipe must be at least 2 inches in diameter.
The discharge pipe must have a check valve and a gate valve (or ball valve) on the discharge side.
The sump cover must be gas-tight and removable.
The ejector pump must be capable of handling solids (typically a sewage ejector, not a clear-water pump).
Discharge connection: The ejector discharge must connect to the building drain or sewer at a point above the elevation of the sump. It cannot discharge directly into a horizontal drain below the sump level.
Inspector’s eye: Inspectors verify the presence of a check valve to prevent backflow, and they confirm that the vent pipe is connected before the sump pump (not after). They also check that the discharge pipe rises above the flood level rim of the sump before turning down.
1.8 Materials and Joints
The IPC specifies approved materials for drainage piping. Common materials include:
Cast iron (hub and spigot, no-hub)
PVC (polyvinyl chloride) — Schedule 40 for drainage
ABS (acrylonitrile butadiene styrene)
Copper (for small diameter, typically 1.5 inches or less)
Galvanized steel (rarely used for drainage, but permitted in some cases)
Joint requirements:
PVC and ABS joints must be made with solvent cement approved for the material.
Cast iron no-hub joints use stainless steel couplings with rubber sleeves.
Transition joints (e.g., copper to PVC) require a dielectric coupling or approved transition fitting.
Prohibited: You cannot mix PVC and ABS with the same solvent cement. Each material has its own cement. Also, you cannot use compression gaskets on PVC drainage pipe unless the pipe is specifically rated for it.
Inspector’s eye: Inspectors check for the proper primer and cement color (PVC primer is purple). They also verify that no cast iron pipe is connected directly to copper without a dielectric union.
1.9 Testing and Inspection
Before a drainage system is concealed or covered, it must be tested.
Water test: The system is filled with water to a head of 10 feet (3,048 mm) above the highest point of the tested section. The water level must not drop for at least 15 minutes.
Air test: For systems that cannot hold water, an air pressure test of 5 psi (34.5 kPa) is used. The pressure must hold for 15 minutes without a drop.
Final test: After all fixtures are installed, a smoke test or peppermint test may be used to detect leaks in the completed system.
Inspector’s eye: Inspectors require that all joints be exposed for testing. They will not allow a system to be covered until the test is witnessed and passed.
Code Navigation (Open-Book Guide)
Use this quick index to find the relevant IPC sections during the exam:
Concept
IPC Location
Definitions (building drain, sewer, etc.)
Chapter 2 (Definitions)
General regulations for drainage
Chapter 7, Section 701
Prohibited connections
Section 701.2, 701.3
Materials for drainage pipe
Section 702
Slope of horizontal piping
Section 704.1, Table 704.1
Minimum pipe sizes
Section 710.1, Table 710.1
Drainage fixture unit values
Table 709.1
Sizing of building drain and sewer
Section 710.1(1), Table 710.1(1)
Cleanouts (location and size)
Section 707, Table 707.5
Offsets and changes in direction
Section 706
Sumps and ejectors
Section 712
Testing of drainage systems
Section 715
Roof drainage (for contrast)
Chapter 11
Exam strategy: When you see a question about slope, go directly to Table 704.1. When you see a question about dfu values, go to Table 709.1. Do not rely on memory for table values — the code is open book, so use it.
Practical Inspection Points (Field Checklist)
Slope check: Place a level on the pipe; the bubble should be off-center in the direction of flow. Measure the drop over 10 feet to verify the minimum slope.
Cleanout access: Ensure cleanouts are not buried behind drywall without an access panel.
No cross-connections: Trace roof drains and downspouts to confirm they do not tie into the sanitary system.
Fitting check: Look for sanitary tees used incorrectly on horizontal runs — this is a common violation.
Sump vent: Confirm the sump has a vent pipe connected to the vent system, not just a screened opening.
Test records: Verify that the water or air test was performed and documented before concealment.
Summary
Sanitary drainage is a core area of the Journeyman Plumber exam. Master the slope table, the dfu values, and the cleanout placement rules. Understand the difference between a building drain and a building sewer. Know which fittings are prohibited. Finally, use the code navigation table to find answers quickly during the exam — speed and accuracy will come from knowing where to look, not from memorizing every number.
