How to Plumb a Bathtub Using 1½” PVC – Step-by-Step Guide

Replacing or installing a new bathtub? One of the most critical—and often overlooked—steps is properly plumbing the drain and overflow system. Many DIYers wonder how to plumb a bathtub using 1½” PVC, especially since this size is standard for residential tub drains in the U.S. Done right, it ensures smooth drainage, prevents leaks, and meets local plumbing codes. In this guide, we’ll walk you through the entire process with clear, actionable steps—even if you’ve never held a pipe wrench before.

Why Use 1½” PVC for Bathtub Drains?

Before diving into installation, let’s clarify why 1½-inch PVC is the go-to choice for bathtub drainage in North America.

According to the International Plumbing Code (IPC), fixture drains for bathtubs must be at least 1½ inches in diameter. This size balances flow capacity with space efficiency under typical bathroom floors.

“A 1½-inch drain can handle up to 31 gallons per minute—more than enough for a standard tub filling at 4–7 GPM,” explains plumbing engineer Maria Lopez, P.E., in a 2023 ASPE (American Society of Plumbing Engineers) bulletin.

PVC (polyvinyl chloride) is preferred because it’s:

• Corrosion-resistant
• Lightweight and easy to cut
• Cost-effective (typically $0.50–$1.20 per foot)
• Compatible with standard tub drain kits

Note: While ABS is also used, PVC is more common in the western and southern U.S., whereas ABS dominates in colder northern regions due to impact resistance. Always check your local code—but for this guide, we’ll focus on Schedule 40 PVC, the residential standard.

Tools & Materials You’ll Need

Gather these before starting:

💡 Pro Tip: Buy a universal tub drain kit (like those from Oatey or Sioux Chief) that includes both the drain shoe and overflow tube—designed specifically for 1½” PVC connections.

Step-by-Step: How to Plumb a Bathtub Using 1½” PVC

Follow these steps carefully. Rushing can lead to leaks or failed inspections.

Step 1: Dry-Fit the Drain Assembly

• Place the tub in its final position (or mock it up if not installed yet).
• Attach the drain shoe to the bottom outlet using plumber’s putty.
• Connect the overflow tube to the side port.
• Measure the distance from the drain shoe outlet to your main waste line (usually in the wall or floor).

⚠️ Important: The horizontal drain arm should slope ¼ inch per foot toward the main stack. For a 24-inch run, that’s a ½-inch drop.

Step 2: Cut & Dry-Assemble PVC Pipes

• Cut 1½” PVC pieces to match your measured distances.
• Use a 90° elbow to connect vertically from the drain shoe, then a horizontal run to the main stack.
• Include a cleanout tee if local code requires it (common in California and Florida).

Dry-fit everything without glue. Ensure the tub sits level and the pipes align without stress.

Step 3: Glue the PVC Joints

1. Prime all surfaces with purple PVC primer.
2. Apply PVC cement evenly.
3. Insert pipe into fitting with a ¼-turn twist to spread glue.
4. Hold for 30 seconds—don’t move!

📌 Fact: PVC cement welds the joint—it’s not just adhesive. A proper bond cures in 15 minutes but reaches full strength in 24 hours.

Step 4: Connect to the Main Waste Stack

• Your 1½” tub drain typically ties into a 2″ or 3″ main vertical stack.
• Use a sanitary tee (not a regular tee!) to prevent siphoning.
• Maintain proper venting within 5 feet of the trap (per IPC Section 906.1).

For more on venting principles, see Wikipedia’s overview of plumbing vents.

Step 5: Test for Leaks

• Plug the main stack downstream.
• Fill the tub with 2–3 inches of water.
• Open the drain and watch all joints for drips.
• If dry after 10 minutes—you’re good!

Common Mistakes to Avoid

Even experienced DIYers slip up here:

• Using 1¼” pipe: Too small—violates code and causes slow drainage.
• Skipping the trap: Every tub needs a P-trap to block sewer gases.
• Gluing too soon: Misaligned pipes = permanent errors.
• Ignoring slope: Flat or back-pitched lines cause standing water.

🛠️ Real-World Example: In a 2024 Home Inspection Report by InterNACHI, 23% of failed bathroom inspections were due to improper tub drain sizing or missing traps.

PVC vs. Other Materials: Quick Comparison

Stick with rigid 1½” PVC unless your inspector says otherwise.

FAQ Section

Q1: Can I use 1½” PVC for both the drain and overflow?

Yes. Most modern tub drain kits use a single 1½” outlet that combines both functions via an internal baffle. Older clawfoot tubs may have separate lines—but still use 1½” for each.

Q2: Do I need a P-trap under the tub?

Absolutely. The P-trap holds water to block sewer gases. It must be installed within 24 inches of the drain outlet and vented properly.

Q3: What’s the maximum distance from tub drain to vent?

Per IPC, the trap arm (horizontal pipe from trap to vent) can’t exceed 5 feet for a 1½” line. Beyond that, you risk siphonage and odor backup.

Q4: Can I glue PVC in cold weather?

Below 40°F (4°C), PVC becomes brittle and glue cures slowly. If unavoidable, use cold-weather PVC cement and allow 48 hours for full cure.

Q5: Is 1½” PVC allowed by code everywhere in the U.S.?

Most jurisdictions follow IPC or UPC, which approve 1½” for tubs. However, always verify with your local building department—some cities (like Chicago) have amendments.

Q6: Should I hire a plumber or DIY this?

If you’re comfortable with basic tools and can pass a pressure test, DIY is feasible. But if walls are closed or venting is complex, hire a licensed plumber—a botched drain can cause mold or sewage backup.

Conclusion

Now you know exactly how to plumb a bathtub using 1½” PVC—safely, legally, and efficiently. With the right materials, attention to slope, and proper gluing technique, your tub will drain smoothly for decades. Plus, you’ll avoid costly callbacks or inspection failures.

If this guide saved you time or confusion, share it on Pinterest, Facebook, or Reddit—your DIY-savvy friends will thank you! Got questions? Drop them in the comments below. Happy plumbing! 🛁🔧