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newSchoolWorks.com › VoTechWorks › Building & Construction › Plumbing & Pipefitting › Drain, Waste & Vent (DWV) Systems: Layout, Installation & Inspection › Lesson 11
BLD-PLUM06-03 · Lesson 11 · 12 clock hours · lab

DWV Testing — Air, Water & Smoke Tests

Objective. Students will perform a code-referenced air pressure test and a water test on their completed rough-in assembly, identify any failures by location, repair them, and document results in a test log.

Why DWV Systems Must Be Tested

A drain, waste, and vent (DWV) system that leaks is not a minor inconvenience — it is a public-health hazard. Sewer gases, including hydrogen sulfide and methane, are toxic and potentially explosive. Contaminated wastewater can saturate wall cavities and building materials before anyone sees a stain. For these reasons, the International Plumbing Code (IPC) and the Uniform Plumbing Code (UPC) both require rough-in testing before walls are closed. An inspector must witness or accept documented proof that the system holds. Passing the test is not optional and the pressure values, hold times, and acceptance criteria are set by code — not by the plumber's judgment.

The Three Recognized DWV Tests

Air pressure test. Compressed air is introduced into the sealed system and held at a code-specified low pressure for a code-specified minimum duration. Check your applicable code for the exact pressure (commonly in the range of a few pounds per square inch) and the required hold time. Because air expands when warm and contracts when cool, temperature changes during the test can affect gauge readings; conduct the test under stable conditions. A drop in gauge pressure indicates a leak somewhere in the system.

Water test. The system is sealed at its lower end and filled with water to the level of the highest opening — typically the top of the stack or the highest vent terminal inside the building. The column of water exerts hydrostatic pressure on every joint below it. The system is observed for a minimum of 15 minutes (verify the exact duration in your applicable code). Any loss of water level, dripping, or wet spot indicates a failed joint.

Smoke test. A non-toxic, non-staining smoke is pumped into the sealed system. Smoke escaping through walls, floors, or fixtures pinpoints the exact location of a leak, including openings that might be missed by air or water alone. Smoke tests are especially useful for locating trap seal failures and improper venting connections. This lab focuses on air and water tests; your instructor will demonstrate the smoke test as a supplemental method.

Safety Before You Touch the Equipment

Sealing the System: Plugs and Inflatable Bags

Every opening in the rough-in assembly must be sealed before testing begins. Mechanical test plugs thread or wedge into pipe ends. Inflatable test bags are inserted into the pipe and inflated to seat against the pipe wall; they are especially useful for sealing a stack inside a fitting without removing a section of pipe. Match plug size to pipe size — using a 3-inch plug in a 4-inch pipe is a test failure waiting to happen. After all openings are sealed, leave one accessible point — typically a cleanout or a capped stub — where the gauge and air supply will connect.

Performing the Air Pressure Test — Step by Step

1. Confirm all openings are sealed. Visually trace every branch, vent, and stub before pressurizing.

2. Connect the hand pump (or low-pressure regulated air source) and a calibrated pressure gauge to the test port.

3. Slowly introduce air until the gauge reads the code-referenced test pressure. Do not rush; rapid pressurization can seat plugs incorrectly.

4. Start your timer for the required hold period.

5. Watch the gauge continuously. Any drop signals a leak.

6. If pressure drops, spray all joints, fittings, and plug edges with soapy water. Bubbles identify the leak location. Mark every leak with a marker or tape flag.

7. Relieve pressure, make the repair, re-pressurize, and repeat the full hold time from zero.

Performing the Water Test — Step by Step

1. Seal the lowest opening — usually with an inflatable bag in the building drain just before the cleanout or test tee.

2. Fill the system through the highest opening, using a hose, until water reaches the top of the stack or the required height.

3. Record the water level (or gauge reading if a standpipe gauge is used) and the exact start time in the test log.

4. Observe for the minimum 15-minute hold period. Walk every accessible joint.

5. Record the water level and end time. Any measurable drop in water level or any visible drip is a failure.

6. Drain the system, locate and repair the leak, and retest.

The Test Log

Every test must be documented. Your test log must include: the date, your name, your partner's name, the pipe material and sizes tested, the test type (air or water), start and end times, start and end gauge or water-level readings, a pass/fail notation for each attempt, a description of any repairs made, and your signature. Inspectors rely on this document. An unsigned or incomplete log is treated the same as a failed test — the wall does not get closed.

Connecting This Lab to Your Credentials

NCCER Plumbing Levels cover DWV installation and testing procedures as core competencies. State journeyman licensing examinations test your knowledge of code-required test methods and acceptance criteria. ASSE Backflow certification, while focused on backflow prevention assemblies, also requires understanding of system integrity testing. Every credential you are working toward expects you to know not just how to test, but why each requirement exists.

Key terms9

air pressure testA DWV system test in which all openings are sealed, low-pressure air is introduced to a code-specified pressure, and the system is monitored for a required hold time; any pressure drop indicates a leak.
water testA DWV test in which the sealed system is filled with water to the highest opening and observed for a minimum period; loss of water level or visible drips constitutes failure.
smoke testA supplemental DWV test in which non-toxic smoke is pumped into the sealed system; escaping smoke pinpoints the exact location of leaks, trap seal failures, or improper connections.
test plugA mechanical device — threaded, wedge-type, or inflatable — inserted into a pipe opening to seal it during pressure or water testing; must match the nominal pipe size.
inflatable test bagA bladder inserted into a pipe and inflated to press against the pipe wall, sealing the opening without requiring access to the pipe end; commonly used inside stacks and building drains.
hydrostatic pressureThe pressure exerted by a column of standing water due to gravity; in a water test, the height of the water column determines the pressure applied to joints below.
test logA written record documenting all test parameters — date, names, pipe sizes, test type, start and end readings, times, pass/fail results, repairs made, and plumber's signature — required for inspection approval.
hold timeThe minimum duration, specified by the applicable plumbing code, during which the system must maintain test pressure or water level without loss to be considered passing.
sewer gasA mixture of gases — including hydrogen sulfide, methane, and ammonia — produced by decomposing waste in a drainage system; toxic, potentially explosive, and the primary reason DWV systems must be leak-free and properly vented.

Worked examples4

1. Your air pressure gauge reads 5.0 psi at the start of the hold period. After the required hold time the gauge reads 4.6 psi. Did the system pass or fail, and by how much did the pressure drop?
  1. Identify start reading: 5.0 psi.
  2. Identify end reading: 4.6 psi.
  3. Calculate pressure drop: 5.0 − 4.6 = 0.4 psi.
  4. Acceptance criterion: zero pressure drop over the hold time.
  5. 0.4 psi drop is greater than zero, so the system fails the air test.
Answer: The pressure dropped 0.4 psi. The system fails; all leaks must be located, repaired, and the full test repeated from the beginning.
2. During a water test, you mark the water level at the top of a standpipe at 48.0 inches above the floor drain invert at the start. After 15 minutes the level reads 47.25 inches. How much water level was lost, and what is the result?
  1. Start level: 48.0 inches.
  2. End level: 47.25 inches.
  3. Loss: 48.0 − 47.25 = 0.75 inches of water column.
  4. Any measurable loss of water level is a failure under the water test.
  5. Result: FAIL — locate and repair the leak, then retest.
Answer: The water level dropped 0.75 inches. This is a measurable loss; the system fails the water test and must be repaired and retested.
3. You are filling a DWV stack for a water test. The stack is a 3-inch diameter PVC pipe. You need to fill it from the sealed bottom to a height of 10 feet (120 inches) to reach the highest opening. Approximately how many gallons of water will be needed? (Use: volume of a cylinder = π × r² × h; 1 gallon ≈ 231 cubic inches; π ≈ 3.1416)
  1. Convert nominal pipe size to radius: 3-inch nominal PVC has an inside diameter of approximately 3.068 inches; radius ≈ 1.534 inches.
  2. Height: 120 inches.
  3. Volume = π × r² × h = 3.1416 × (1.534)² × 120.
  4. (1.534)² = 2.353 square inches.
  5. 3.1416 × 2.353 = 7.393 square inches (cross-sectional area).
  6. 7.393 × 120 = 887.2 cubic inches.
  7. Convert to gallons: 887.2 ÷ 231 ≈ 3.84 gallons.
  8. Note: actual volume needed will be higher because branches and fittings add volume; this calculation is for the stack pipe alone.
Answer: Approximately 3.84 gallons to fill the 3-inch stack pipe alone to a 10-foot height. Additional water is needed for branches and fittings connected to the stack.
4. You seal a DWV system and introduce air. The code-referenced test pressure for your jurisdiction is expressed as a gauge pressure. You pump slowly and the gauge needle moves from 0 to the required test pressure in about 90 seconds. Your partner says you should have pressurized faster to save time. Who is correct, and why?
  1. Slow, controlled pressurization allows test plugs and inflatable bags to seat properly against the pipe walls before full pressure is reached.
  2. Rapid pressurization can dislodge plugs, especially inflatable bags that have not fully expanded, causing a plug to eject under pressure — a safety hazard.
  3. Slow pressurization also allows you to detect a large leak (rapid gauge drop) before full pressure is reached, avoiding unnecessary pressure on a clearly compromised joint.
  4. Conclusion: you are correct to pressurize slowly.
Answer: You are correct. Slow, controlled pressurization is the safe method. It allows plugs to seat fully and lets you detect major leaks early, reducing the risk of plug ejection or joint damage.

The math in this lesson2

Learners convert stack volume from cubic inches to gallons (÷231) and compute pressure and water-level drops.
N-Q.1G-GMD.3
Brush up in the math halls at newSchoolWorks.com:
In class: Instructor demonstrates plugging all openings with test plugs and inflatable bags, connecting a hand pump or low-pressure air source, and reading the gauge; class discusses why test pressure and duration follow code, not personal preference. · Student pairs plug their assembly, pressurize to the code-referenced air test pressure, and monitor the gauge for the required hold time; any pressure drop triggers a soap-bubble search for leaks, which are marked, repaired, and retested. · Students also perform a water test by filling the stack to the highest opening and observing for 15 minutes; they record gauge or water level readings at start and end in a formatted test log that mirrors what an inspector expects.
Materials: Completed rough-in assembly from Lessons 9–10, DWV test plugs (1½-inch, 2-inch, 3-inch, 4-inch), inflatable test bags, hand air pump, pressure gauge, soapy water in spray bottle, water hose, test log form, IPC/UPC codebooks
Check: Air test: zero gauge drop over the required hold time. Water test: no visible leaks over 15 minutes. Both tests must pass; log must be complete with times, pressures, and student signature. Failures require repair and retest — lab is not signed off until both tests pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NCCER Plumbing — DWV Systems and Testing
1. During an air pressure test of a DWV rough-in assembly, the gauge shows a steady drop over the hold period. What is the correct next action?
State Journeyman Plumber — Code Compliance
2. Which of the following best explains why DWV test pressures and hold times are set by the plumbing code rather than left to the plumber's judgment?
NCCER Plumbing — DWV Systems and Testing
3. An inflatable test bag is inserted into the building drain to seal the system for a water test, but the pipe is a 4-inch line and the bag selected is rated for 3-inch pipe. What is the most likely result?
State Journeyman Plumber — Inspection Documentation
4. A student completes both the air and water tests successfully but submits a test log that lists only the pass/fail result, not the start and end readings or the times. An instructor reviewing the log should:
NCCER Plumbing — Safety and PPE
5. Why must a plumber wear eye protection when inflating a test plug inside a DWV pipe?
State Journeyman Plumber — Inspection and Testing
6. During a water test, a student fills the stack to the required height and observes the system for 15 minutes. The water level does not drop and no drips are visible, but one hub joint near the floor feels slightly damp. What should the student do?
NCCER Plumbing — Safety
7. Hydrogen sulfide and methane in sewer gas are hazards because they are, respectively:
NCCER Plumbing — DWV Systems and Testing
8. A smoke test is most useful for locating which of the following DWV problems that an air pressure test might not easily pinpoint?
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