Capping a sink waste pipe is a crucial skill in the toolkit of any DIY enthusiast or homeowner. This seemingly simple task plays a vital role in various home maintenance and renovation scenarios. Whether you’re remodelling your kitchen, dealing with a damaged pipe, or altering the purpose of a space, knowing how to properly cap a sink waste pipe can save you time, money, and prevent potential water damage. This skill is invaluable and will save you the plumber call out charge, so in this article, we will delve into the reasons for capping a sink waste pipe and show you how.

Sink Pipe Waste Cap

Why Do You Need to Cap a Sink Waste Pipe?

There are several scenarios where capping a sink waste pipe becomes necessary. The most common include:

  1. Home Renovations: When remodelling a kitchen or bathroom, sinks may be temporarily removed or relocated. Capping the waste pipe prevents debris and dust from the renovation process from entering the plumbing system.
  2. Damaged Pipes: If a sink waste pipe is damaged and awaiting repair, capping it can prevent water leakage and further damage to your home.
  3. Converting Space Usage: In cases where a sink is no longer needed, such as converting a kitchenette to a storage area, the waste pipe should be properly capped to avoid leaks and odours.

Do you Need to Cap the Waste Pipe Permanently?

Understanding the difference between temporary and permanent capping is crucial, as each serves a different purpose:

  • Temporary Capping: This is often used during renovations or repairs. It involves placing a removable cap on the waste pipe, which can be easily taken off once the work is completed or the sink is reinstalled. This method is ideal for short-term solutions where future access to the pipe is needed.
  • Permanent Capping: When a sink is being permanently removed or if the pipe is no longer in use, a permanent cap is installed. This method involves sealing the pipe more securely, often using adhesives or soldering, to ensure that it is watertight indefinitely. This is the preferred method when the pipe will not be used again in the foreseeable future.

Step-by-Step Guide to Capping a Sink Waste Pipe

Below are the steps for capping a waste pipe temporarily followed by the additional steps to take if you want to make it permanent.

What You Need

  • Pipe cutter or a small-toothed hacksaw
  • Measuring tape
  • Clean rag or towel
  • Sandpaper or a natural abrasive cloth
  • Temporary pipe cap (appropriate size for your pipe)
  • Spanner (optional, depending on cap type)

Step 1 – Cut off the Water Supply

Before commencing any plumbing work, it is essential to locate and turn off the main water supply valve. This valve is typically situated in the basement, garage, or outside near the street. Turning the valve clockwise will halt the flow of water to all the taps and fixtures in your home, ensuring no water escapes when you cut the pipe.

To relieve any residual pressure in the pipes, open a tap at a lower level in your home.

Step 2 – Take Pipe Measurements

Accurately measure the diameter of the drain pipe using a measuring tape. This measurement is crucial for selecting the correct size cap for the pipe. Once you have determined the diameter, mark the section of the pipe where the cap will be fitted. It’s important to choose a clean, straight section of the pipe to ensure a secure fit.

Use a marker or chalk to clearly indicate the area on the pipe.

Step 3 – Cut Through the Pipe

Utilise a pipe cutter or a small-toothed hacksaw to carefully cut through the marked area of the pipe. When using a hacksaw, ensure the cut is as straight as possible to facilitate a snug fit for the cap. Exercise caution during this step to avoid any jagged edges.

Step 4 – Clean the Pipe

Once the pipe is cut, it’s important to clean both the inside and outside of the cut pipe. Use a clean rag or towel to remove any debris, dust, or residual water. This step is crucial for ensuring a clean surface for the cap to adhere to. This is also a good time to check and remove any blockages in the pipe.

Step 5 – Sand the Edges

After cleaning, use sandpaper or a natural abrasive cloth to smooth the cut edges of the pipe. This process helps in removing any burrs or rough spots, ensuring a clean and even surface for the cap to be mounted on.

Step 6 – Mount the Cap

Place the temporary cap over the open end of the pipe. Ensure that the cap fits snugly and is aligned correctly. If the cap requires it, use a wrench to tighten it and ensure a secure fit. This step is vital to prevent any leaks.

Step 7 – Final Check

The final step is to ensure that the cap is securely in place and there are no leaks. Check around the cap for any signs of water leakage. If everything appears secure and dry, the capping process is complete.

Permanent Capping

Additional Instructions to cap your waste pipe permanently:

Step 1 – Apply Primer

After the pipe has been cleaned and the edges sanded, the next step is to apply a primer. This is a crucial step in the process of permanent capping. The primer should be applied evenly to both the outside of the pipe and the inside of the permanent cap. The purpose of the primer is to prepare the surfaces, enhancing the adhesion of the PVC cement. Ensure that the primer is applied thoroughly but avoid over-application, which can cause pooling.

Step 2 – Apply PVC Cement

Once the primer has dried, which usually takes only a few minutes, apply PVC cement to both the primed area of the pipe and the inside of the cap. PVC cement is a type of solvent that melts a thin layer of the PVC, allowing the pieces to fuse together. When applying the cement, make sure it covers the entire primed area but is not overly thick. After applying the cement, quickly join the cap to the pipe.

It is essential to align the cap straight and push it onto the pipe until it is fully seated. The cement sets quickly, so this step must be done promptly and accurately.

Step 3 – Hold and Secure

After joining the cap to the pipe, hold it in place firmly for several seconds. This pressure ensures a strong bond as the cement sets. Be cautious not to twist or move the cap during this time, as it could compromise the seal. Once you are confident the cap is securely in place, use a clean rag to wipe away any excess cement from around the joint. This not only gives a neater finish but also allows for a clearer view during the final inspection.

Step 4 – Final Inspection

Allow sufficient time for the cement to dry completely; this usually takes several hours. After the drying period, conduct a thorough inspection of the capped pipe. Check to ensure that the cap is securely attached and that there are no visible gaps or misalignments. Once you are satisfied with the installation, turn the water supply back on.

Observe the capped joint for any signs of leakage. If no leaks are detected and the cap remains firmly in place, the permanent capping process is successfully completed.

Troubleshooting Common Issues

Even with careful installation, issues can arise when capping a sink waste pipe. Knowing how to address these problems is key to a successful project.

Dealing with Leaks

Ensuring a tight seal is crucial when capping a pipe. If you notice a leak, first check the tightness of the cap. For temporary screw-on caps, tightening with a spanner might solve the issue. For permanent caps, inspect the seal for any gaps or misalignments. If the leak persists, it may be necessary to remove the cap, clean the area, and reapply primer and cement, ensuring each step is meticulously followed.

Removing a Cap

To remove a temporary cap, simply loosen it with a spanner and gently pull it off the pipe. For permanent caps, the process is more complex. You may need to cut the pipe again below the capped area. Always wear safety gear and take precautions to avoid damaging the remaining pipe.

Maintenance and Care

Regularly inspect capped pipes for signs of wear or leakage. Keep the area around the cap clean and dry to prevent corrosion or buildup. If you notice any changes in the pipe or cap, address them promptly to maintain the integrity of the plumbing.


Knowing how to cap a sink waste pipe is an invaluable skill in home maintenance. This guide provides the necessary steps and tips to ensure a successful capping, whether temporary or permanent. Approach this task with confidence and remember that a little preparation and attention to detail can lead to effective and long-lasting results.

Tips for Capping Off a Sink Waste Pipe Infographic
Tips for Capping Off a Sink Waste Pipe Infographic

Plumbing Wizard Tips

“Always measure the pipe diameter precisely before cutting; an accurate cut is essential for a proper fit and effective seal!”

“Select a cap material that matches your pipe, such as PVC caps for PVC pipes, to ensure a better fit and a more effective seal!”

“After capping the pipe, conduct a leak test by turning the water back on and observing for moisture, to address any leaks promptly!”

“Keep essential tools like a pipe cutter, sandpaper, measuring tape, and the right cap at hand for a smooth and efficient capping process!”

Frequently Asked Questions

Can you cap a waste pipe?

Yes, you can cap a waste pipe, which is often done during renovations or when a plumbing fixture is removed.

How do you seal an unused drainpipe?

To seal an unused drainpipe, clean and dry the pipe end, then cap it with an appropriate-sized cap using PVC cement for a permanent seal or a rubber cap for a temporary solution.

How do you cap a water pipe under a sink?

To cap a water pipe under a sink, first shut off the water supply, then cut the pipe, ensuring a clean, straight cut. After that, fit a cap over the pipe end, securing it with a clamp or using PVC cement, depending on the type of pipe and cap.

What is the best way to cap off PVC water pipe?

The best way to cap off a PVC water pipe is to use a PVC cap. Apply PVC primer and cement to both the pipe and the inside of the cap, then press the cap onto the pipe, holding it in place for a few seconds to ensure a strong bond.


Lee Pearce is not just a master plumber; he’s a veritable Plumbing Wizard. With over 30 years of experience in the trenches of pipes and drains, Lee has become the go-to sage for DIY plumbing, saving homeowners thousands in potential call-out charges. As the founder of Plumbing Wizard, he’s dedicated to demystifying the complexities of home plumbing, offering easy-to-follow advice that stands the test of time and pressure. His online blog is a treasure trove of tips, tricks, and tutorials that empower everyday individuals to take charge of their home’s plumbing health. Lee’s practical wisdom is not just about fixing leaks; it’s about imparting confidence and self-reliance. When he’s not writing or elbow-deep in a plumbing project, Lee is passionate about educating the next generation of DIYers, ensuring that practical skills are passed down and preserved.

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