How to Air Test DWV Plumbing: 4″ Combo, 10ft @ 10 PSI

So, you’ve just finished installing a new section of your Drain-Waste-Vent (DWV) system—a 4-inch combo fitting spanning about 10 feet—and now it’s time for the crucial air test. You’re not alone if you’re feeling a bit nervous. A failed test can mean costly rework and project delays. But don’t worry! This guide will walk you through how to air test DWV plumbing 4 combo 10ft pressure correctly, safely, and in full compliance with modern plumbing codes. Whether you’re a seasoned contractor or a confident DIYer, you’ll have the confidence to pass inspection on the first try.

What Is a DWV Air Test and Why Is It Required?

Before we dive into the “how,” let’s clarify the “why.” A DWV air test is a non-destructive method used to verify that your newly installed drainage and vent piping is airtight and free of leaks. This is critical because:

• Health & Safety: Leaks in a DWV system can allow dangerous sewer gases like methane and hydrogen sulfide into your living space.
• Code Compliance: The International Plumbing Code (IPC) and Uniform Plumbing Code (UPC) mandate testing of all new DWV installations before they are covered up or put into service.
• System Integrity: A properly sealed system ensures efficient drainage and proper venting, preventing slow drains, gurgling sounds, and even sewer backups.

According to the IPC Section 312, the standard test pressure for a DWV system is 10 pounds per square inch (PSI) of air pressure. This test must be held for a specified duration, typically 15 minutes, with no loss of pressure.

What Tools and Materials Do You Need?

Having the right gear is half the battle. Here’s your complete checklist:

• Air Test Plug (Test Ball): A 4-inch inflatable test plug is essential for sealing the end of your pipe run. Make sure it’s rated for at least 15 PSI.
• Air Compressor: A small, portable compressor (like a 1-2 gallon pancake model) is perfect for this job. You don’t need anything industrial.
• Pressure Gauge: A 0-15 PSI or 0-30 PSI gauge with a Schrader valve (like a tire valve) is ideal. Many test plugs come with one built-in.
• Hose & Fittings: A short length of air hose and a chuck to connect your compressor to the test plug.
• Teflon Tape or Pipe Dope: For sealing any threaded connections on your test setup.
• Safety Glasses: Always protect your eyes when working with pressurized systems.

Pro Tip: Double-check that your test plug is the correct size. A 4-inch plug is designed for a 4-inch pipe’s inside diameter. Using the wrong size is the #1 reason for a failed test.

Step-by-Step Guide: How to Air Test Your 4″ Combo, 10ft Run

Follow these steps precisely to ensure a successful test.

Step 1: Prepare the System

Seal off every opening in your 10-foot DWV section except for one. This includes:

• All fixture outlets (toilets, sinks, showers).
• The main stack connection at the top.
• Any cleanouts within the test section.

You can use test caps, rags, or even your hand (temporarily) to seal these. The goal is to create a single, closed chamber.

Step 2: Install the Test Plug

Insert your 4-inch test plug into the lowest accessible opening of your 10-foot run—usually the end of the horizontal drain line. Inflate it just enough to create a snug seal against the pipe wall. Do not over-inflate, as this can damage the plug or the pipe.

Step 3: Connect Your Air Source

Attach your air compressor to the test plug’s valve using your hose and chuck. Ensure all connections are tight.

Step 4: Pressurize the System

Turn on your compressor and slowly introduce air into the system. Watch your pressure gauge carefully. Stop pumping air once you reach exactly 10 PSI. Over-pressurizing can damage fittings or cause a blowout.

Step 5: Conduct the Test

Once you hit 10 PSI, turn off the compressor and disconnect the hose. Start your timer for 15 minutes. During this time, do not touch or adjust anything. Simply observe the pressure gauge.

Step 6: Evaluate the Results

• Pass: If the pressure gauge holds steady at 10 PSI (or shows a negligible drop of less than 1 PSI due to temperature changes) for the full 15 minutes, your system is airtight!
• Fail: If the pressure drops significantly (e.g., below 8 PSI), you have a leak. You’ll need to locate it (often by listening for hissing or using soapy water on joints) and repair it before retesting.

For more information on the standards governing these systems, you can refer to the general principles of plumbing.

Common Mistakes to Avoid (And How to Fix Them)

Even experienced plumbers can slip up. Here are the most frequent pitfalls:

FAQ Section

Q1: What is the correct pressure for an air test on a DWV system?

The universally accepted standard in the US, as defined by the IPC and UPC, is 10 PSI. This pressure must be held for a minimum of 15 minutes with no significant loss.

Q2: Can I use water instead of air for this test?

Yes, a water test (hydrostatic test) is also a valid method. However, an air test is generally preferred for its cleanliness, speed, and ease of use, especially for shorter runs like your 10-foot section. Water tests are often used for underground or vertical stacks.

Q3: My pressure dropped by 2 PSI. Did I fail?

Not necessarily. A small pressure drop can be caused by a change in ambient air temperature (Charles’s Law). If the drop was gradual and you can’t find any audible or visible leaks, it may still be acceptable. However, for a definitive pass, aim for zero loss. When in doubt, consult your local inspector.

Q4: Do I need a permit to perform this test?

You typically need a plumbing permit for the entire installation, and the air test is a required part of the final inspection for that permit. You don’t need a separate permit just for the test itself.

Q5: What if I can’t find the leak after a failed test?

Start by checking the most common failure points: the test plug seal, glued PVC joints (especially if glue wasn’t applied evenly), and threaded connections. Use a spray bottle with soapy water on suspect joints; bubbles will form at the leak site.

Q6: Is this test required for a simple bathroom remodel?

If your remodel involves installing any new DWV piping—even a single new vent or drain line—it must be tested. The scope of your project doesn’t exempt you from this safety-critical step.

Conclusion

Mastering how to air test DWV plumbing 4 combo 10ft pressure is a fundamental skill that ensures your plumbing work is safe, durable, and up to code. By following this clear, step-by-step process, you can avoid callbacks, pass inspections with flying colors, and give your clients (or yourself!) peace of mind.

Don’t let a simple test stand in the way of a successful project. With the right preparation and attention to detail, you’ve got this! If you found this guide helpful, please share it with a fellow plumber or DIYer on social media. Let’s build a community of safe and skilled tradespeople!