Leaking pipes under a sink are one of the most common household issues, yet they are often ignored until the damage spreads. A constant drip not only wastes water and increases your utility bill, but it can also rot cabinetry, warp flooring, and promote mold growth. While calling a plumber is always an option, learning how to replace pipes under sink is a practical skill that saves time and money. With the right tools and a methodical approach, this project is straightforward for any homeowner.
Assessing the Damage and Gathering Tools
Before you rush to the hardware store, take a moment to identify the exact source of the leak. Is it coming from the drain connection, the faucet supply lines, or the trap itself? Often, water stains or mineral deposits provide clear clues. Once the culprit is identified, you will need specific equipment to complete the job efficiently. Having these items ready prevents mid-project trips to the hardware store and keeps your workspace organized.
Essential Toolkit
- Adjustable wrench or basin wrench
- Channel-lock pliers
- Screwdriver set
- Pipe tape (Teflon tape)
- Bucket or shallow tray
- Rags or shop towels
- Replacement pipes or fittings
Safety and Preparation
Safety is the foundation of any successful home repair, and under-sink work is no exception. The first step is to turn off the water supply valves located beneath the sink. If these valves are stuck or missing, you may need to turn off the main water line to the house. After shutting off the water, open the faucet to drain the remaining pressure and water from the lines. Place the bucket directly under the pipes to catch residual water and debris, protecting your cabinet and floor from damage.
Disassembling the Old Pipes
With the water fully shut off and the area prepped, you can begin removing the old piping. Most under-sink setups consist of three main components: the supply lines (hot and cold), the P-trap or drain tailpiece, and the connections to the faucet and drain. Use your wrench to loosen the slip nuts connecting the pipes. Before fully removing anything, position your bucket to catch any dripping water. Carefully loosen the connections one at a time, pulling the pipes away slightly to inspect for stubborn debris or hidden leaks.
Measuring and Selecting Replacements
Accuracy is critical when installing new pipes. Even a slightly mismatched length or diameter will lead to leaks or improper drainage. Use a cloth or flexible tape to measure the center-to-center distance of the supply valves for the new supply lines. For the drain components, ensure the new pipes match the diameter of the existing ones—usually 1 1/4 inches for the drain and 3/8 or 1/2 inches for the supply lines. When purchasing parts, take the old component to the store for a direct comparison rather than relying solely on packaging labels.
The Installation Process
With the new pipes ready, installation is the reverse of removal, but with a focus on creating a proper seal. Before threading the new supply lines, wrap the threads with pipe tape to ensure a tight, leak-free connection. Hand-tighten the nuts first, then use your wrench to secure them firmly—avoid over-tightening, as this can crack fittings or strip threads. For the drain system, assemble the P-trap loosely, slide it into place, and then tighten the slip nuts by hand. The goal is to align the pipes correctly without forcing them, which can cause cracks or misalignment.
Testing for Leaks
Once all connections are secure, restoring water supply is the moment of truth. Slowly turn the shutoff valves back on and inspect each connection for immediate drips. It is crucial to check the entire system while the water is running, as minor leaks are often invisible when the flow is off. After confirming the supply lines are dry and secure, run water in the sink, drain, and garbage disposal to test the drain assembly. Watch the P-trap area closely for several minutes to ensure standing water does not cause a slow leak. If you discover a drip, turn the water off, re-tighten the specific fitting, and test again until the system is completely dry.
