How To Plumb A Bathroom Sink With PEX – Step-by-Step Guide (2025)

Why PEX Is the Smart Choice for Your Bathroom Sink (And Why You’re Reading This)

You’re standing in your bathroom, staring at a leaky faucet or a rusted copper pipe, wondering: “Can I fix this myself?” Maybe you’ve heard PEX is easier than copper, cheaper than stainless steel, and doesn’t require soldering—but you’re not sure where to start.

You’re not alone. Over 68% of new home builds in the U.S. now use PEX piping, according to the Plastic Pipe and Fitting Association (PPFA), and for good reason: it’s flexible, freeze-resistant, and installs up to 50% faster than traditional materials.

If you’re looking to plumb a bathroom sink with PEX, you’re making a smart, modern choice. This guide will walk you through every step—no prior plumbing experience needed. We’ll cover tools, safety, connections, and even how to avoid the #1 mistake 82% of DIYers make (spoiler: it’s not tightening enough… or tightening too much).

Let’s get your sink flowing smoothly—safely and for life.

What Is PEX, and Why Is It Better Than Copper for Bathroom Sinks?

Before we dive into installation, let’s clear up a common confusion: What exactly is PEX?

PEX stands for cross-linked polyethylene—a flexible, high-density plastic tubing designed specifically for water distribution. Unlike rigid copper pipes, PEX bends around corners without elbows, resists corrosion, and won’t develop pinhole leaks from aggressive water chemistry.

Here’s how it stacks up:

Source: Wikipedia – PEX

Expert Insight:

“PEX is the most reliable material for residential water lines today. Its flexibility reduces stress points, and its resistance to scale and chlorine makes it ideal for bathrooms.”
— John M. Smith, Master Plumber & ASSE Certified Instructor, 28+ years experience

Bottom line: PEX is cheaper, faster, and more durable. If you’re replacing an old sink or building new, PEX is the winner.

What Tools and Materials Do You Need to Plumb a Bathroom Sink With PEX?

You don’t need a professional toolkit. Here’s your simple, affordable PEX plumbing kit:

✅ Materials:

• ½-inch PEX tubing (Type A, B, or C—Type A is most common for DIY)
• PEX crimp rings or stainless steel clamps (match your fitting type)
• PEX-to-faucet adapters (typically ⅜” compression or ½” NPT threaded)
• Shut-off valves (ball valve recommended)
• Pipe cutter or PEX cutter
• PEX crimp tool or pinch clamp tool (depending on fittings)
• Tape measure
• Adjustable wrench
• Plumber’s tape (Teflon tape)
• Bucket and towels (for spills)

💡 Pro Tip: Buy a PEX expansion tool kit if you plan on doing more plumbing projects. It’s pricier upfront but works with all PEX types and creates the strongest seal.

⚠️ Safety First: Turn off your main water supply before starting. Test for pressure by opening a faucet upstairs. No water? You’re good to go.

Step-by-Step: How to Plumb a Bathroom Sink With PEX (7 Easy Steps)

Follow this sequence exactly. Skipping steps causes leaks—and trust us, you don’t want to re-do this after drywall is up.

Step 1: Shut Off Water & Drain the Lines

Locate your home’s main water shutoff valve (usually near the water heater or meter). Turn it clockwise until tight. Then, open the sink faucet to drain any remaining water. Place a bucket under the sink to catch drips.

Step 2: Remove the Old Supply Lines

Use an adjustable wrench to disconnect the old copper or flexible braided lines from the shut-off valves under the sink. If they’re corroded, spray with penetrating oil and wait 10 minutes before twisting.

Step 3: Install New Shut-Off Valves (If Needed)

Most older homes have outdated angle stops. Replace them with ¼-turn ball valves—they’re more reliable and easier to operate. Screw them into the existing ½” NPT threads using plumber’s tape (3–4 wraps clockwise).

🔧 Pro Tip: Use PEX-to-threaded adapters with built-in shut-offs. One-piece units save time and reduce leak points.

Step 4: Measure and Cut PEX Tubing

Measure from the shut-off valve to the faucet inlet. Add 6 inches for slack and maneuvering. Use a PEX cutter (not a hacksaw!) for a clean, square cut. A jagged edge = poor seal.

Cut two pieces:

• One from shut-off valve to faucet (length A)
• One from shut-off valve to other faucet line (if double sink)

Step 5: Attach PEX to Shut-Off Valves

Slide a crimp ring onto the end of the PEX tubing (before inserting). Insert the PEX fully into the valve’s barbed fitting until it hits the stop. Use your crimp tool to compress the ring evenly around the tubing. You should hear a distinct “click.”

✅ Check the Seal: After crimping, tug gently on the tube. It shouldn’t pull out. If it does, cut and start over.

⚠️ Critical Detail: Crimp rings must be placed 1/4 inch from the end. Too close = weak seal. Too far = risk of bursting.

Step 6: Connect PEX to the Faucet

Most modern faucets have ¾” NPT female threads. Use a PEX-to-compression adapter (e.g., ½” PEX to ⅜” compression). Wrap Teflon tape clockwise around the male threads (3–4 layers), then screw the adapter into the faucet inlet. Tighten with an adjustable wrench—snug, not brutal.

💡 Expert Rule: “Hand-tighten first, then give it a quarter-turn with the wrench. Over-tightening cracks the faucet’s internal valve.” — Mike Ruiz, Plumbing Contractor, Austin, TX

Step 7: Test for Leaks and Turn Water Back On

Slowly reopen the main water supply. Let water run for 30 seconds to flush debris. Then, turn on the sink faucet. Check every connection point for drips:

• PEX-to-valve
• Valve-to-wall
• Adapter-to-faucet

If you see even a single drop, shut off water and re-crimp or re-tape. Don’t ignore it. A slow drip can rot your cabinet in weeks.

✅ Final Check: Run hot and cold water for 5 minutes. Feel the PEX tubing—it should stay cool. If it’s warm, you may have a partial blockage or improper slope.

PEX vs. Copper: Real-World Cost & Time Comparison

Let’s say you’re replacing a sink in a 1990s home. Here’s what you’re really paying:

Data compiled from HomeAdvisor 2024 U.S. Plumbing Cost Reports

Bottom Line: PEX saves you $200+ and 4+ hours. And if you ever need to move the sink later? Just cut and re-crimp. With copper? You’re calling a pro.

FAQ: Your Top 6 Questions About Pluming a Bathroom Sink With PEX

Q1: Can I use PEX for both hot and cold water lines to my sink?

Yes! PEX is rated for temperatures up to 200°F (93°C)—well above typical hot water heater output (120–140°F). Type A, B, and C PEX are all approved for hot/cold use. Just use red PEX for hot, blue for cold (for easy identification).

Q2: Do I need a permit to plumb a bathroom sink with PEX?

In most U.S. municipalities, minor plumbing repairs like sink supply lines don’t require a permit—unless you’re altering drain lines or moving fixtures. Always check your local building code (visit your city’s website). PEX is approved in all 50 states under the Uniform Plumbing Code (UPC).

Q3: What’s the difference between PEX-A, PEX-B, and PEX-C?

• PEX-A (most flexible): Made with peroxide method. Best for expansion fittings.
• PEX-B (most common): Made with silane method. Works with crimp/clamp fittings.
• PEX-C (least common): Made with electron beam. Rarely used in homes.

👉 For DIY sink plumbing, PEX-B with crimp fittings is the sweet spot: affordable, reliable, and widely available.

Q4: Can I connect PEX directly to a faucet without an adapter?

No. Faucets use threaded metal inlets (⅜” or ½” NPT). PEX is plastic and flexible—you need a transition fitting. Use a PEX-to-compression adapter or PEX-to-threaded nipple. Never force PEX into a metal thread.

Q5: How long do PEX connections last?

Properly installed PEX connections last 40–50 years—longer than most sinks. The key? Use quality fittings (SharkBite, Uponor, Viega) and avoid overtightening. Avoid cheap hardware store brands—many fail within 5 years.

Q6: Is PEX safe for drinking water?

Yes. All PEX tubing sold in the U.S. must meet NSF/ANSI 61 standards for potable water. Look for the NSF mark on the tubing. No chemicals leach into your water under normal conditions.

Final Thoughts: Why This DIY Project Will Save You Money (and Stress)

Plumbing a bathroom sink with PEX isn’t just a repair—it’s an upgrade. You’re replacing outdated, brittle copper with a system designed for the 21st century: flexible, leak-resistant, and future-proof.

You’ve saved money on materials. You’ve saved time on installation. And most importantly—you’ve gained confidence.

This isn’t magic. It’s mechanics. And now, you know how to do it right.

👉 Found this guide helpful? Share it with a friend who’s drowning in leaky pipes! Tag them on Pinterest or Facebook with: “I fixed my sink with PEX—and it was easier than I thought!”