How to Do the Plumbing for a Bathtub – Step-by-Step Guide

Thinking about installing or replacing a bathtub? You’re not alone—over 1.2 million U.S. homeowners tackle bathroom renovations each year, according to the National Association of Home Builders (NAHB). But plumbing for a bathtub isn’t just about hooking up pipes; it’s about precision, code compliance, and avoiding water damage that could cost thousands. In this guide, you’ll learn exactly how to do the plumbing for a bathtub the right way—whether you’re a confident DIYer or just trying to understand your plumber’s work.

Is Bathtub Plumbing Something You Can DIY?

Many homeowners ask: “Can I really handle bathtub plumbing myself?” The answer depends on your experience, local regulations, and the complexity of your bathroom layout.

According to the U.S. Department of Housing and Urban Development (HUD), nearly 68% of minor plumbing issues stem from improper installation during renovations. While simple tasks like connecting a drain can be DIY-friendly, supply lines and venting often require permits and inspections. Always check your local building codes—some states, like California and New York, mandate licensed plumbers for any wet-wall work.

💡 Pro Tip: If you’re unsure, do the rough-in yourself (with measurements and dry-fit pipes) and hire a plumber just for final connections and inspection sign-off. This saves money and ensures safety.

Tools & Materials You’ll Need

Before touching a wrench, gather the right gear. Here’s a checklist:

• Adjustable wrench & basin wrench
• Pipe cutter or hacksaw
• Teflon tape & pipe joint compound
• Level & tape measure
• 1.5″ PVC or ABS pipe (for drain)
• ½” copper or PEX supply lines (hot & cold)
• Bathtub drain kit (with overflow)
• Plumber’s putty or silicone sealant
• Shutoff valves (if not already installed)

📌 Note: Always turn off the main water supply before starting. Even a small drip can cause major damage behind walls.

Step-by-Step: How to Do the Plumbing for a Bathtub

Step 1: Position the Tub and Mark Drain Location

Place the bathtub in its final position before connecting pipes. Most tubs sit on a mortar bed or support frame—never on dry subfloor alone. Once secure, mark the exact center of the drain hole on the floor (usually 14–16 inches from the back wall).

✅ Precision Matters: A misaligned drain can cause slow drainage or leaks. Use a laser level if possible.

Step 2: Install the Drain Assembly

1. Apply plumber’s putty around the underside of the drain flange.
2. Insert the flange into the tub’s drain hole from above.
3. From below, thread the drain body up and tighten with a wrench.
4. Connect the overflow mechanism per manufacturer instructions—this links to the main drain via a horizontal pipe inside the tub wall.

⚠️ Warning: Use only the gaskets and parts included in your drain kit. Mixing brands can cause poor seals.

Step 3: Connect the Drain Pipe to the Waste System

• Cut a 1.5″ PVC or ABS pipe to connect the tub’s drain outlet to your home’s main waste stack.
• Maintain a ¼-inch per foot slope toward the main drain—critical for proper flow (per International Plumbing Code §706).
• Use a P-trap under the tub to prevent sewer gases from entering your bathroom.
• Secure all joints with PVC cement (for PVC) or approved glue (for ABS).

🔗 Learn more: Traps and vents are essential for safe plumbing—Wikipedia explains the physics simply.

Step 4: Install Supply Lines for Hot & Cold Water

• Run ½” PEX or copper lines from your home’s water supply to the tub’s faucet location.
• Use angle stop valves (shut-offs) near the faucet for easy maintenance.
• Insulate hot water lines to reduce heat loss and prevent condensation.
• Keep supply lines at least 6 inches above the drain to avoid accidental siphoning.

Step 5: Test for Leaks Before Closing Walls

• Turn on the water supply and let it run for 10–15 minutes.
• Check all joints, the P-trap, and the overflow connection with a dry paper towel—any moisture = leak.
• Fill the tub halfway and pull the drain stopper to test drainage speed and seal.

📊 Stat: The average homeowner saves $300–$600 by doing rough-in work themselves—but only if no leaks occur post-install.

Common Mistakes to Avoid

When to Call a Professional

While this guide empowers you, call a licensed plumber if:

• Your home has galvanized steel pipes (prone to corrosion)
• You’re relocating the tub to a new wall
• Local code requires permits for plumbing work
• You smell sewer odors after installation

The U.S. Bureau of Labor Statistics reports that licensed plumbers earn certifications in backflow prevention and IPC compliance—skills that prevent long-term hazards.

FAQ Section

Q1: How long does bathtub plumbing take?

A: For a DIYer with basic skills: 4–8 hours. Professionals typically complete it in 2–3 hours, plus inspection time.

Q2: Can I reuse old supply lines?

A: Only if they’re PEX or copper and in perfect condition. Braided stainless hoses degrade over time—replace them for ~$15.

Q3: What’s the difference between ABS and PVC drain pipes?

A: ABS is black, more impact-resistant, and common in cold climates. PVC is white, quieter, and easier to glue. Both are code-approved, but don’t mix them—they require different adhesives.

Q4: Do I need a vent for my bathtub?

A: Yes. Every fixture must be vented to equalize air pressure. Without it, water drains slowly and the P-trap can siphon dry.

Q5: Can I install a tub without an overflow?

A: Technically yes, but it’s not recommended and may violate code. Overflows prevent flooding if the faucet is left running.

Q6: How do I know if my drain is properly sloped?

A: Use a 4-foot level. Lift one end until the bubble is centered—this equals a ¼” drop per foot. Measure the gap under the pipe at the far end.

Conclusion

Now you know how to do the plumbing for a bathtub safely, efficiently, and up to code. Whether you’re renovating a guest bathroom or upgrading your master suite, proper plumbing ensures comfort, prevents damage, and adds value to your home.

If this guide saved you a service call or gave you the confidence to start your project, share it with a friend on Facebook, Pinterest, or Twitter! Got questions? Drop them in the comments—we’re here to help you succeed, one pipe at a time. 💧🔧