Understanding Test Tees: Why Fittings II and V Make Drainage System Testing Easy

A quick reality check for anyone wiring their knowledge toward a solid plumbing career: you’ll run into fittings that aren’t just about moving water from point A to B. Some of them are about making sure the system performs under pressure, stays leak-free, and is easy to inspect later on. One such fitting is the test tee. If you’re tallying up which fittings are used to test drainage lines, here’s the straight answer you’ll want to keep in mind: the test tees are type II and type V.

What exactly is a test tee?

Think of a test tee as a regular pipe tee with a special job. It’s designed to give you a cleanout access point right in the drainage run, plus a place to attach testing equipment without having to tear the system apart. The key features you’ll notice are:

• A cleanout port or cap that lets you get inside the pipe to inspect, clear, or verify flow.

• A horizontal branch that makes it convenient to connect a testing device—whether you’re conducting a water test or an air pressure test.

• A robust design so it can withstand the testing process without compromising the rest of the drainage system.

In many plumbing schematics or material charts you’ll encounter, fittings are grouped and numbered (I, II, III, IV, V, and so on) to indicate their shape, orientation, and function. When the topic turns to testing, the fittings that are designated II and V pop up as the “test tees.” It’s all about making testing straightforward and accessible, not about complicating the layout.

II and V: the practical duo

Let’s demystify what makes type II and type V test tees special, beyond the generic idea of a tee with a cleanout.

• Type II test tee: This one is commonly used where you want a direct, easy-to-access cleanout on a drainage line. The branch is typically oriented so you can attach a test hose, pressure gauge, or other testing device without fighting gravity or working around a crowded area. Materials usually match the rest of the drain (PVC, CPVC, ABS, etc.), so you’re not introducing dissimilar metals that could lead to corrosion or other compatibility issues.

• Type V test tee: This variation often emphasizes a cleaner real estate in the wall or under a floor, with a cleanout that’s straightforward to reach during inspections and maintenance. The branch may be positioned to align with standard testing equipment or to fit within a compact space, which is helpful in tight installations like behind a vanity or in a utility chase. As with Type II, the branch gives you a hub for attaching gauges, test balls, or other devices needed to verify the system’s integrity.

Why this matters in real-world work

The practical value is simple: testing a drainage system before you cover everything up is smart. Leaks, misdrops, or blocked paths can be expensive to fix after the walls go up. The test tees pocket a ready-made access point and a convenient connection point for measuring performance, which makes it easier to satisfy codes and inspectors. That’s the real reason you’ll see II and V singled out in many references—it’s not about one fancy feature, but about a dependable, standardized way to test.

How to use a test tee during a drainage test

You don’t have to be a rocket scientist to use these fittings correctly, but a plan helps. Here’s a straightforward approach that people in the field tend to follow.

• Plan the test around the system layout. Identify where the main drain runs, where the fixtures tie in, and where a test tee can serve as the best access point without crowding the space. If you’re rough-in wiring in, you’ll often place these tees where future service is easiest to reach.

• Install with the right materials. Match the test tee to the pipe material in the run (PVC to PVC, ABS to ABS, copper to copper, etc.). If a connection needs a solvent cement or mechanical coupling, apply it per the manufacturer’s instructions and local code requirements. A solid, clean connection is your best defense against false failures.

• Prepare for testing. During a drainage test, you’re looking to verify that the line holds pressure (or a specified water column) and that there are no leaks. Attach your testing device to the cleanout in the test tee. For a water test, you’ll fill the system until solidly primed, ensuring any air pockets are pushed out. For an air test, you’ll follow the code's recommended procedure to introduce a controlled amount of air.

• Conduct the test and observe. Watch for steady pressure readings without drops, and inspect for any visible leaks along joints and fittings. If you see movement, pause to recheck sealants, gaskets, or the connection to the test equipment. It’s not unusual to re-test after a small adjustment.

• Finish and restore. Once you’ve confirmed the run is sound, you’ll close the cleanout cap, remove testing equipment, and finalize connections. If you’re in a retrofit scenario, this is the moment to ensure you’ve preserved access for future maintenance while keeping the line visually clean.

A note about safety and codes

Code bodies vary, and your local rules will dictate the exact test pressures, duration, and whether you’re using water or air tests. The overarching idea is to protect the public health and ensure long-term performance. Using the test tee as intended—keeping the cleanout accessible and the testing port unobstructed—helps maintain that standard.

Why this knowledge is useful in the field

Beyond the immediate job, understanding test tees gives you a leg up on proper system design and inspection. It’s part of knowing how a drainage system behaves under pressure, how it can be diagnosed if something goes wrong, and how to ensure future access for maintenance. It’s the kind of knowledge that shows up in job briefs and field reports, and it’s a reliable indicator that you’re thinking about the system as a whole—not just the fixtures.

Common mistakes to avoid

Even seasoned pros can trip over the same small missteps. Here are a few to keep in mind when working with II and V test tees:

• Skipping the cleanout access. If the cap or plug isn’t easily removable, you defeat the whole purpose of the test tee.

• Using incompatible fittings. Mixing materials without proper transition components can lead to leaks or corrosion down the line.

• Overlooking slope and alignment. A tee that’s not aligned with the run can create where leaks hide or air pockets form.

• Ignoring code requirements. The test method (water vs. air), duration, and pressure targets vary; skipping this can cause a failed inspection later.

A few practical tips

• Label the test tee clearly in your notes. It saves time when you’re reviewing plans or handing off to a colleague.

• Keep a small kit handy: cleanout caps, replacement gaskets, thread seal tape, and a basic tester. It’s the “just in case” kit that saves you a trip back to the truck.

• When space is tight, consider the geometry. The horizontal branch on a test tee should align with your testing equipment without forcing you to contort around elbows or other fittings.

Relating it to other fittings you’ll meet

While test tees are all about testing and maintenance access, you’ll still encounter standard tees, reducing tees, wyes, and sanitary tees in day-to-day work. Each serves a different purpose—some prioritize correct flow direction, others aim to ease future cleaning. Understanding how II and V fit into the broader family helps you read plans more confidently and spot issues before they become real problems.

In a nutshell

When you come across the label II and V in a piping plan, you’re looking at the test tees—fittings designed to make testing drainage runs practical and reliable. They’re built with a cleanout feature and a convenient horizontal branch so you can attach gauges and testing devices, verify that the system holds pressure, and keep maintenance accessible down the line. It’s a small piece of the puzzle, but it’s exactly the kind of detail that saves time, reduces headaches, and keeps systems performing as they should.

If you’re mapping out a project or reviewing a scheme, keep the test tees in mind as a touchpoint for quality and future serviceability. They’re not flashy, but they’re dependable—and in the plumbing world, that steadiness is worth more than it might seem at first glance. And as you gain experience, you’ll start to see how those little decisions—like where to place a test tee or how to route a branch—add up to smoother, more reliable work on real jobs.

So next time you see II and V in a diagram, you’ll know exactly what they’re for and why they matter. It’s one of those practical details that separates the good work from the great work—the kind of nuance that shows up in the reports, the audits, and, ultimately, in the homes you help keep dry and safe.