Pipe Plug Best Practices

When performing testing and repair of drainage, waste and vent systems, consider these guidelines for using pipe plugs

Pipe Plug Best Practices

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Proper testing of DWV (drainage, waste and vent) systems is an essential component of the reliable and efficient operation of residential plumbing.

Contractors must follow best practices to maintain these systems’ functionality and avoid potential issues such as blockages, leaks, and improper ventilation. 

When you test DWV systems with water, smoke or air, pipe plugs are a common tool to isolate specific sections for inspection or pressure testing purposes. When using a pipe plug, you'll typically perform one of three essential tasks:

  1. Stopping the flow: This involves placing a pipe plug to halt the flow in a pipeline or opening. For this task, a blocking plug is typically used. These can also serve as back plugs for sewer air tests. Test balls don't have a bypass and are designed to do one job: blocking (sealing) a pipe.
  2. Bypassing the flow: This involves using a pipe plug to redirect or bypass the flow running through the pipeline. Bypass/muni ball plugs are specifically designed for situations where a repair is needed while wastewater must continue to flow. These plugs are capable of handling high back pressure in applications such as water mains, force mains, and industrial lines. A muni ball plug features a bypass tube that runs through the plug, allowing the user to divert effluent through the tube. By using an adapter cap, the muni ball plug can also be converted to complete an air test.
  3. Performing a low-pressure air test: This involves conducting a test on a new pipeline before putting it into service or testing an already in-service pipeline for leaks. During this process, a test pump is used to inflate the test plugs, sealing off the pipeline. By introducing low-pressure air into the pipeline, any potential leaks can be identified.

When using a pipe plug for testing, it’s critical to follow the manufacturer’s instructions carefully to ensure proper insertion and a secure, airtight or watertight seal. 

Here are some recommended guidelines when using pipe plugs during DWV system testing. By adhering to these guidelines, contractors can ensure that homeowners have peace of mind, knowing their residential plumbing systems are functioning correctly.


To ensure a successful testing process, it is crucial to prioritize safety, read the instructions provided by the plug manufacturer, and understand the proper usage and safety precautions specific to the plug you are using. Using a plug that fails for any reason can result in bodily injury, property damage, or even death. Additionally, unsafe practices can also lead to severe injuries or fatalities. 

  • Choose the right pipe plug

Determine the appropriate size and type of pipe plug to use for the specific application. Pipe plugs have a minimum and maximum sealing size range. 

The first step is to determine the inside diameter of the pipe to be plugged. Then choose the plug that matches the ID of the pipe for that application. Here at Cherne, some plugs can be used for multiple pipe sizes, but they should be used only on a pipe whose diameter falls within that size range. When in doubt, call the customer service help desk.

  • Determine the maximum back pressure

It’s important to determine the maximum back pressure that the plug must withstand. Back pressure refers to the pressure (air or liquid) in front or behind the plug. Never exceed the plug’s back pressure rating. The latter is defined in pounds per square inch or feet of head. Simply read the gauge pressure for psi. For feet of head, calculate height of water over the centerline of the plug. 

  • Use a calibrated gauge

Failure to use calibrated gauges can result in over-inflation or under-inflation of the plug, leading to plug failure. It’s essential to monitor inflation and back pressure using only calibrated pressure gauges and the appropriate hoses. Also, always do this monitoring, as well as inflating or deflating the plug, from outside the danger zone. (See below.) Cherne does not recommend using compressors for inflating smaller plugs.

  • Clean and inspect the plug and pipe

Plugs must be cleaned and inspected before and after each use. Do not use a plug if it has any signs of wear or deterioration. It’s important to note that all natural rubber products degrade over time, even if they are used infrequently, are properly stored, and show no external signs of damage.

To clean plugs, use mild soap and water, and store them in a dry place away from sunlight. After each use, inspect the plug for any signs of damage, such as cuts, abrasions, punctures, bulges, cracks, corrosion, loose or damaged fittings and components, or leaks. If any damage is found, do not use the plug again.

Additionally, remove any debris or foreign substances before placing the plug. An unclean pipe can reduce the plug’s ability to hold back pressure and may cause damage during placement or inflation.

  • Always be aware of the danger zone

Never enter the danger zone while a plug is in use. A danger zone area expands outwardly in a cone shape from where the plug is. The total force exerted on a pipeline plug is directly proportional to both the pressure and the pipeline area. The amount of force behind a plug can be overwhelming. 


The operation of pipe plugs involves careful insertion, inflation, testing, and removal. By following proper procedures and adhering to manufacturer instructions, you can ensure safe and effective testing while minimizing the risk of damage or accidents.

  • Insert the pipe plug: Insert the pipe plug into the access point and inflate or expand it, depending on the type of plug. Be sure to follow the manufacturer’s instructions for insertion and expansion. Never over- or under-inflate the plug. Position the plug into the pipe at a distance at least equal to the pipe diameter and use the correct media while inflating.
  • Perform the test: Once the pipe plug is securely in place and fully inflated or expanded, perform the desired test, such as a water- or low-pressure air test or a smoke test. Adhere to the recommended procedures outlined by the manufacturer when performing the testing. This may include the appropriate inflation pressure, monitoring the pressure during the test, and following specific steps for inflation and deflation. Deviating from these procedures can lead to inaccurate results and compromised safety.
  • Inspect for leaks: While conducting the test, carefully monitor the test area for any signs of leaks or pressure loss. This involves visually inspecting the system, checking for any visible water or air leaks, and paying attention to any unusual sounds or pressure drops.  If you notice any leaks or pressure loss, stop the test immediately and take the necessary steps to address the issue. This may involve tightening fittings, repairing damaged pipes, or replacing faulty components. Continuing the test with leaks can lead to inaccurate results and compromise the effectiveness of the testing process.
  • Remove the pipe plug: After completing the test, application, or use of the plug, it is important to remove the plug safely and in a controlled manner. Begin by standing outside the danger zone and releasing all back pressure behind the plug. Once all back pressure is released, relieve the plug pressure — again, standing outside the danger zone — until the plug is completely deflated.  It is crucial to always release the back pressure from the pipe before deflating the plug. Deflating the plug before releasing the back pressure can result in the plug dislodging at an extreme velocity, posing a safety risk.

About the Author: Sean Comerford is a technical applications manager at Oatey Co. He is a third-generation tradesman with nearly 20 years of plumbing experience, including serving as the lead plumber for commercial/residential new-construction, service and fire protection jobs. He holds a State of Ohio Fire Protection License for Sprinkler and Standpipe. He can be reached at technical@oatey.com.


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