Plumber's Licensing Exam: Sanitary Drainage

More emphasis is placed on the proper design of a sanitary drainage system than almost any other part of a plumbing code, with the possible exception of ensuring a potable water supply. It could be argued that sanitary drainage systems have contributed more toward the elimination and/or reduction of disease than the medical profession. By reducing the population’s exposure to pathogens, the health of the nation has been vastly improved.
 

Objectives
- Discuss the importance of a properly designed drainage system
- Explain the correct connection techniques for similar pipes and fittings, as well as the connection methods for dissimilar pipes and fittings
- Recognize the appropriate materials for the different parts of a drainage system
- Learn to properly size a sanitary drainage system
- Identify the proper places for cleanouts and manholes
- Detect when a backwater valve is necessary
- Pinpoint the proper piping and design for subdrains, sumps, and sewage ejectors

Key Terms:
building drain
building sewer
DFU
hydraulic jump
local vent
Transite pipe
General Requirements

Modern sanitary drainage systems and clean water supplies accomplished more toward the suppression of these dangerous scourges than the science of medicine did. The system name arises from the job these drainpipes do. They help keep our personal environments sanitary. Therefore, the name is more appropriate than one would have thought. The whole idea of the plumbing codes is to ensure that sanitation is maximized through well-designed plumbing systems. (Refer to IPC 701.1–701.3; UPC 713.0–713.6

Real-Life Situation: Manuel and Will have the job of roughing in the drainage piping for the new Springfield Old Elms Community, a retirement complex of apartments and townhouses. The Ace Plumbing Company estimator, Sophia, has done none of the sizing of the drainage piping. She quoted the job using rule-of-thumb averages. It is up to Manuel and Will to be certain they load the different sections of drainage piping with the proper DFU load or risk inspection failures and plugged drains.
All buildings that have plumbing fixtures installed in them must be connected to the public sewer if there is one. This rule creates some turmoil when a locality installs a sewer system where none existed before. Many individuals will want to cling to their own septic tank; not for sentimental reasons, but in order to save the expense of installing the building sewer. The rule exists to prevent individual sewage disposal systems from possibly polluting or contaminating nearby properties, water supplies, or waterways by leaking into storm sewers. The individual sewer systems are mainly uncontrolled after the original installation, and local governments prefer being able to provide a safe, sanitary system by ensuring that all sewage goes directly to a sewage treatment plant through the public sewer.
Individual buildings under different ownership must have their own connection to the public sewer. If a complex of buildings is under one ownership, which is common with commercial properties, buildings can share a single connection to the public sewer. This approach strives to eliminate conflicts that can arise when trying to determine which owner (or owners) is responsible for repairs and maintenance of a sewer lateral being shared by different buildings with different owners.

Allowable Sewage
Sewage cannot be released into any part of the environment until it has been rendered harmless through some form of sewage treatment. This provision prevents any individual or public/private entity from dumping sewage directly into the soil or any waterway. This has gone a long way toward cleaning up many waterways and wetlands. Only methods approved by the local Authority Having Jurisdiction can be used to treat sewage. (Refer to IPC 701.4–701.9; UPC 714.0– 714.5)

No material that will hinder the function of a sewage treatment plant can be introduced into a sewer system. This includes chemical waste and any items that can clog a system. Nothing that can break down, attack, or damage the drainage piping is allowed. When an industrial plant, for example, has chemical waste, it must be neutralized before sending it through drains into the sewage system.
Another often-overlooked provision prevents water that is at a temperature higher than 140°F from being sent down the drainage piping. High-temperature waste can damage piping through stress and strain from expansion and, of course, plastic drainpipes can be warped by high temperatures. This regulation also keeps any steam exhausts from being connected to the sewer system.

Piping Materials
It is essential that quality materials are used in drainage systems. Both aboveground and especially belowground systems remain in service for many decades. Sewer piping must be able to withstand physical stress and be resistant to the liquids and gasses that flow through them. (Refer to IPC 702.1–702.6; UPC 701.0– 701.2.3)

Aboveground Piping
The table below displays all the materials that are permitted for aboveground drainage piping. Brass pipe, copper or copper alloy pipe, galvanized steel pipe, and glass pipe are only allowed in aboveground applications. The other materials shown in the table are also allowed to be used in underground building drain applications.

Belowground Piping
The second table below, which lists the approved materials for underground building drain and vent piping, contains most of the same materials as the first table for aboveground drainage piping, with a few exceptions. Asbestos-cement pipe is allowed for use as the underground building drain, but not for use above ground.

For the underground building sewer pipe, the list of accepted materials once again changes. Some additional configurations of PVC and ABS pipe are allowed; concrete pipe is allowed; only types K and L copper pipe are allowed; polyethylene (PE), which is one form of polyolefin pipe, is allowed; and finally, that old (very old) drainage standby, vitrified clay tile pipe, aka terra-cotta pipe, is allowed for use as building sewer pipe (Table below).

An important fact about building sewers that may very well be on your licensing test is that it is allowable to lay a storm sewer side by side with the sanitary sewer. There is far less risk of a sanitary sewer leaking into a storm sewer than a sanitary sewer leaking into a potable water system.
The grade, or pitch, of a drainage system is essential to ensuring that waste flows properly though the sewage system. A velocity of approximately 2 feet per second is the best speed for wastewater to flow in order to keep suspended solids moving along with the water. A minimum pitch of 1/2-inch per foot for drains 21/2 inches in diameter reaches that critical velocity. For drains of 3 inches to 6 inches in diameter, 1/8-inch per foot is the minimum slope allowed, and 1/16-inch per foot is the minimum slope for pipes that are 8 inches or larger. One should note that no maximum pitch is stated in the codes; however, for good piping practice, a pitch of no more than 1/2-inch per foot should be maintained.
Never reduce the diameter of a drainage pipe in the direction of flow. Never reduce the diameter of a drainage pipe in the direction of flow. Yes, I repeated that. It’s important, and no, a 4 × 3 inch water closet connection is not considered to be a reduction in size by both codes. Why? you ask. Take a look at the outlet size of a water closet bowl. It will range somewhere between 17/8 inches up to about 21/4 inches. The closet flange is made larger in order to create a larger surface area and steadier mounting surface for the sealing ring and the closet bolts.

Caution: Hydraulic jump can be observed in the water at the base of a dam or even in a flat-bottomed sink when a stream of water from the faucet lands in the sink. Water “piles up” at the point where the velocity of the flow can no longer keep the water moving at the same pace and the body of water slows to the pace determined by flow in a horizontal plane. When wastewater piles up just past the base of a stack where the flow transitions from a rapid vertical descent to a slower horizontal flow, wastewater would flow backward up a branch that is connected within 10 pipe diameters of the stack. The consequence is the depositing of solids in the branch, which creates the potential for blockage of the branch.
Connection of horizontal branches to the horizontal drain at the base of a stack is prohibited until a distance equal to 10 times the diameter of the stack is reached. If a connection is closer than that to the base of the stack, waste from the stack will be pushed up the connected branch by the turbulence at the base of the stack known as hydraulic jump.
Dead ends in drains are prohibited. A dead end is most often created when capping drainpipes that are taken out of service. A discontinued drain must be cut and capped within 24 inches of an active drain in order to meet code. In new work, extension of a cleanout beyond 24 inches is permitted and drainage pipes for future plumbing are permitted to go beyond 24 inches.
The IPC (Section 702.6) establishes the minimum thickness for lead bends and traps at 0.125 inch. Nowadays, lead pipes and fittings are rarely installed, generally in a chemical piping system.
 

Piping Joints
Just as the weakest link determines the strength of the chain, proper joints maintain the integrity of a piping system. Correct joining methods must be used to ensure not only a sturdy system, but also that the piping system will pass inspection. (Refer to IPC 705.1– 705.22; UPC 704.0–705.3.3)

Connections between Similar Fittings and Pipe
ABS plastic—allowable joining methods:
- Elastomeric seals

Elastomeric seals can be used to connect ABS to ABS or to other piping materials.
- Solvent cement

The only approved solvent cementing is ABS solvent cement to connect ABS to ABS.
- Threaded joints

Threaded joints can be used to connect ABS to ABS or to any other “threadable” material.
Asbestos cement pipe—commonly referred to as Transite pipe—can only be joined using the asbestos cement sleeve coupling with elastomeric rings. When connecting asbestos cement pipe to other materials, mechanical joints utilizing elastomeric couplings are commonly used, although the plumbing code does not recognize this coupling method.
Brass pipe—can be connected to other brass pipe by brazing; mechanical joints, which include elastomeric seals and brass ferules or compression rings; and by welding.
Cast iron—caulked oakum and lead joints, compression gaskets, and mechanical joints are the approved methods for joining cast-iron pipe.
Concrete pipe—an elastomeric ring is the only approved joining method.
PVC plastic—mechanical joints, solvent cementing using purple primer and clear cement, and threaded connections are permitted.
Copper pipe—brazing, mechanical connections, soldering, and threading are the approved connections for copper pipe.
Glass pipe—bolted compression couplings, or caulked joints when connecting glass pipe to a cast-iron hub are permitted.
Steel pipe—threading and mechanical joints are permitted.
Lead pipe—wiped joints and burned joints are approved for lead pipe.
Vitrified clay tile pipe—only elastomeric seals are to be used.
PE pipe—heat-fusion and mechanical joints are approved.
Polyolefin pipe—heat-fusion and mechanical joints are the permitted joining methods.

Connections between Dissimilar Fittings and Pipe
Copper to cast iron—use a ferrule, or soil pipe adapter, to connect copper to cast iron. The adapter can then be caulked or installed with a compression gasket.
Copper to galvanized steel—threaded fittings with dielectric properties must be used.
Cast iron to galvanized steel—a caulked joint or mechanical elastomeric coupling may be used.
Plastic pipe to other materials—threaded fittings can be joined, or in the case of cast iron, a caulked joint is permitted.
Lead pipe to other materials—a wiped joint to a caulking ferrule or approved threaded fitting.
Glass pipe to other materials—adapter couplings containing a TFE seal.
Stainless steel drainage pipe—approved mechanical couplings may be used.
Drainage slip joints—elastomeric rings are approved.

Use of Fittings
Table below shows the allowable positions in which fittings can be used. In general, one can expect that if there is a possibility of waste or wastewater being thrown in an upstream direction in a fitting, the position for that fitting will not be allowed. The point is to ensure a relatively smooth flow of waste from the fixture to the sewer with the least turbulence and opportunity for blockage. (Refer to IPC 706.1–706.4; UPC 706.1–706.4

A heel-inlet quarter bend can be used unless it serves a water closet. Only a high heel fitting can be used for a wet venting application. Side-inlet quarter bends are permitted.

Tips
Tee wyes that sit on their back with the branch in a vertical position are not permitted for use when waste is flowing down the vertical pipe. This position is, however, allowed if the vertical pipe is used exclusively as a vent.
 
Some prohibited connections include cement, concrete, mastic, hot bituminous joints, nonapproved fittings, elastomeric rolling O-rings (when used to connect different diameter pipes), solvent cementing different types of plastic pipes, and saddle fittings.

Cleanouts
Blockages in a drainage system are virtually unavoidable. Cleanouts provide the necessary access to the interior of the drainage pipes through threaded plugs, without the need to cut pipes to gain access. (Refer to IPC 708.1–708.3.2; UPC 707.0–707.10)

Cleanouts must be placed in the following locations:
- In all horizontal drains not more than 100 feet apart.
- In building sewers less than 8 inches in diameter, and not more than 100 feet apart.
- When a horizontal drain, a building drain, or a building sewer with a diameter less than 8 inches has a change of direction of more than 45 degrees, a cleanout is required. No more than one cleanout is required in any 40-foot length of pipe, even if there is more than one change in direction greater than 45 degrees.
- The base of every soil stack or waste stack must have a cleanout.
- A cleanout must be located near the connection between the building drain and the building sewer. If there is a cleanout on a 3-inch or larger soil stack within 10 feet of the connection between the building drain and the building sewer, no other cleanout is necessary.
If a cleanout is in a crawl space or other space with less than 24 inches of clearance, the cleanout must be brought up to an accessible grade. In addition, a cleanout cannot be used for a fixture connection unless it is approved and there is another cleanout available to service the area.
All cleanouts must be the same size as the pipe served, up to 4 inches. Pipes larger than 4 inches can have 4-inch cleanouts.

Manholes
When a manhole is part of a building drain, in other words, inside the building, it must have a gas-tight seal and the cover must be secured. This is done to prevent the escape of sewer gasses inside the building and to help prevent incidental access to the manhole.
For building sewers greater than or equal to 8 inches in diameter, manholes must be installed within 200 feet of the connection with the building drain, and after that, no more than 400 feet apart. Building sewers greater than or equal to 8 inches in diameter must also have a manhole installed at every change in direction of the pipe.

Fact: Water flowing down a vertical stack adheres to the walls of the pipe, leaving an open central column of air. The water also flows downward in a clockwise spiral, which is caused by the rotation of the earth. In the southern hemisphere, the rotation is counterclockwise.
 
Sizing
Sizing a drainage system is an exercise in chart reading and some basic math, which you can refresh in this guide. Using the charts below, you can determine the required size of any portion of a drainage system.

The table below gives you the drainage fixture unit (DFU) value of the individual fixtures. Add up the fixtures on a particular branch and you can easily find the pipe size needed by looking at the tables below. They will also help you figure the maximum DFU load that can be put on stacks. Table 9.6 gives you the DFU values for fixture drains and traps. (Refer to IPC 709.1–710.2; UPC 702.0–703)

Let’s look at an example.

A two-story building has two offices on the first floor, each with one water closet and one lavatory. In the custodian’s closet, there is a service sink. On the second floor are four apartments, each with a kitchen sink and a full bathroom consisting of a water closet, a bathtub, and a lavatory. Start on the second floor. All of the apartments will drain down a single soil stack to the building drain. Each bathroom counts as 5 DFUs, even though the water closet is 3, the tub is 2, and the lavatory is 1. That adds up to 6, but the bathroom group counts as 5 since all fixtures are not expected to be used at the same time.

The kitchen sink accounts for 2 DFUs.

If you look at the table above, you will see that a 21/2-inch pipe would be enough for an apartment drainpipe. However, when you look at Table 9.7 you can see that the minimum pipe size allowed for a water closet is 3 inches, so each apartment must drain with a 3-inch pipe. If the branch from each apartment ties together before entering the soil stack, the horizontal drain carrying all four of the apartment drains must be 4 inches since the combined DFU load of the four apartments is 28 DFUs. A 3-inch horizontal branch can only carry up to 20 DFUs, but the 4-inch branch can carry 90 DFUs as the total load from one branch interval, being the second floor in this case. As we enter the vertical soil stack, it would appear that we can reduce our stack size to 3 inches since a 3-inch stack can handle 48 DFUs and we are only sending it 28 DFUs. We know we cannot do this though, because we can never reduce the diameter of a drainage pipe in the direction of flow. That leaves us with continuing on with a 4-inch stack. Obviously, there are other considerations that go into drain sizing than simply the sizes on the charts.


How many DFUs do the first floor fixtures add up to? For the two water closets: 3 + 3 = 6 DFUs. For the two lavatories: 1 + 1 = 2 DFUs. One service sink equals 2 DFUs. So the total DFU load for the first floor is 10. The first floor requires a 4-inch drain.

The total DFU load for the building is 38 DFUs [(4 × 7) + (2 × 3) + (2 × 1) + 2 = 38 DFUs]. Once again, we are looking at a situation in which a reduction in the size of the building drain would be appropriate since a 3-inch building drain at 1/4-inch per foot slope can carry 42 DFUs, as shown in the table. We will stick with the 4-inch building drain since we can never reduce the diameter of a drainage pipe in the direction of flow.
Keep in mind that if you are doing a complete or a partial rough-in of drainage piping for fixtures that will not be installed at this time, but might be in the future, those DFU values must be included in your sizing calculations just as if the fixtures were being installed now.

Sumps and Ejectors
The material used for sump pumps and ejector pumps, discharge piping, and other fittings shall be rated for maximum system operating pressure and temperature, and where (when?) buried in the earth they shall be suitable for that purpose.
Whenever possible, drains must drain by gravity to the building sewer. When a drain is too low to drain by gravity, it can drain into a sump where the effluent is collected to await being lifted up to the gravity building drain or building sewer by a sewage ejector pump. Sump pumps are now permitted to connect to the drainage system at the soil stack, waste stack, or horizontal branch drain. The sump must be tightly sealed and a vent must terminate either through the roof of the building or into a stack vent in the building that terminates in the open air. The pump must operate automatically. A check valve followed by a full-opening valve are required on the discharge pipe of the ejector pump. The tightly sealed sump must allow access to the pump through a removable cover. The sump itself must be a minimum of 18 inches in diameter and 24 inches deep, but must be sized according to the load. Effluent cannot rise to within more than 2 inches of the top of the sump before the automatic controls start the pump. (Refer to IPC 712.1–712.4.2; UPC 710.1–710.710.13)
A macerating toilet system must be installed according to the manufacturers’ instructions.

Healthcare Drainage Piping
Healthcare facilities require specialized fixtures, and unique provisions are needed to keep high-infection-risk plumbing safe to the patients, the staff, and the public. (Refer to IPC 713.1–713.11.4)
Bedpan washers must connect to the drainage system in a similar way to a water closet and they must be vented with a local vent. Except when it is connected to only one fixture, the base of a local vent must have a trap and a drain connection to the waste stack, which is the same size as the local vent. The trap of a local vent must be primed at each use of the bedpan washer.
Sterilizers, steamers, and condensers must drain through an indirect waste system.
Vacuum systems must be installed so that medical personnel can easily monitor their operation. Vacuum systems must operate at all times. Therefore, backup electricity must be available, and a second pump must be installed so vacuum service is never disrupted.
Vacuum collectors must be connected directly to the drainage system. Indirect wastes are not allowed for these due to the risk of airborne pathogens.

Backwater Valves
Occasionally, a municipal sewer system can become plugged and all the sewage from your neighbors’ buildings can back up into your building drain and up through your fixtures, overflowing gallons and gallons of wastewater in your building. In the determination of backwater valve protection from sewage backflow, the use of the finish flood elevation where the fixtures are installed rather than the flood-level rim of the fixture provides a new point of reference.