Planning a compact bathroom with just a sink and a toilet? You’re not alone—many homeowners, especially in tiny homes, ADUs (Accessory Dwelling Units), or basement conversions, opt for this minimalist setup to maximize space and budget. But how to plumb a bathroom with sink and toilet only can feel overwhelming if you’ve never touched a pipe before. Don’t worry—we’ll walk you through it clearly, safely, and efficiently, so you can get it right the first time.
Why Choose a Two-Fixture Bathroom?
Before diving into pipes and fittings, it helps to understand why this setup is so popular. According to the U.S. Census Bureau, over 20% of new single-family homes built in 2024 included at least one half-bath (toilet + sink only). These spaces are cost-effective, require less square footage, and meet basic hygiene needs without full shower infrastructure.
A two-fixture bathroom is ideal for:
Guest bathrooms
Basement remodels
Home offices with private access
Tiny homes or backyard studios
And yes—you can do the plumbing yourself if you follow local codes and best practices.
What Tools and Materials Do You Need?
Getting started requires the right gear. Here’s a checklist:
Tools:
Pipe cutter or hacksaw
Adjustable wrench
Basin wrench (for tight sink spaces)
Tape measure
Level
Plumber’s putty or silicone sealant
Teflon tape
Materials:
½-inch PEX or copper supply lines (for water)
3-inch PVC drain pipe (for toilet)
1½-inch PVC drain pipe (for sink)
P-trap (for sink)
Wax ring (for toilet)
Shut-off valves (angle stops)
Vent pipe (or air admittance valve if allowed locally)
Step-by-Step Guide: How to Plumb a Bathroom with Sink and Toilet Only
Step 1: Plan Your Layout
Measure your space carefully. The standard clearance:
In front of toilet: 21 inches minimum (30″ recommended)
Side of toilet to wall: 15 inches from centerline
Sink to adjacent wall: At least 4 inches
Sketch a simple floor plan showing drain locations, supply lines, and venting paths. Remember: drain lines must slope downward at ¼ inch per foot toward the main stack.
Step 2: Install the Drain System
Start with the toilet drain, as it’s the largest (3-inch pipe). Connect it to the main soil stack or existing waste line. Use a closet flange secured to the subfloor—this is critical for stability.
Next, install the sink drain (1½-inch PVC). It must connect upstream of the toilet’s trap arm to prevent siphoning. Include a P-trap under the sink to block sewer gases.
⚠️ Warning: Never connect a sink drain directly into the back of a toilet—that’s a code violation and health hazard.
Step 3: Add Venting
Every fixture needs ventilation to equalize pressure and allow smooth drainage. Options:
Traditional vent: Runs vertically through the roof (most reliable)
Air Admittance Valve (AAV): A mechanical vent that opens under negative pressure (allowed in many U.S. jurisdictions for single-fixture vents)
If using an AAV, install it at least 4 inches above the flood rim of the highest fixture—usually the sink.
Step 4: Run Water Supply Lines
Use ½-inch PEX tubing (flexible, freeze-resistant, easy to install) for both fixtures:
Toilet: Cold water only. Connect to a 3/8″ compression fitting on the fill valve.
Sink: Hot and cold lines. Use angle-stop valves under the sink for easy shutoff.
Leave 6–8 inches of extra tubing coiled for future adjustments.
Step 5: Install Fixtures
Toilet: Place a new wax ring on the flange, lower the toilet straight down, and secure with bolts. Don’t overtighten—cracking the porcelain is common.
Sink: Mount the faucet first, then set the sink in place. Seal edges with silicone. Connect supply lines and P-trap.
Step 6: Test for Leaks and Drainage
Turn on water slowly. Check all connections.
Flush the toilet 3–5 times. Watch for leaks at the base.
Run sink water for 1 minute. Ensure no gurgling (a sign of poor venting).
Fill the sink and drain it quickly—water should flow smoothly without backup.
DIY saves significant money—but only if done correctly. If you’re unsure about venting or drain slopes, consult a licensed plumber for a 1-hour consultation ($75–$150).
FAQ Section
Q1: Can I plumb a sink and toilet on the same drain line?
Yes, but with conditions. The sink drain can tie into the horizontal branch of the toilet drain only if it’s upstream of the toilet’s trap and properly vented. Never connect below the toilet trap.
Q2: Do I need a separate vent for each fixture?
Not necessarily. In a two-fixture bathroom, you can often use a common vent if the fixtures are within 5 feet of each other (per IPC Section 908). Alternatively, an AAV can serve both if installed correctly.
Q3: What’s the minimum distance between a toilet and sink?
The IPC requires 15 inches from the center of the toilet to any side wall or obstruction, and 30 inches of clear space in front. The sink should be at least 4 inches from the side wall and not interfere with toilet use.
Q4: Can I use PEX for both hot and cold water lines?
Absolutely. PEX is approved for all residential potable water systems in the U.S. Just use red for hot, blue for cold, and insulate lines in unheated spaces to prevent freezing.
Q5: How do I know if my plumbing passed inspection?
After installation, your local building department may require a rough-in inspection (before walls are closed) and a final inspection. They’ll check slope, venting, fixture spacing, and leak-free operation.
Q6: Is an AAV (Studor vent) legal everywhere?
No. While allowed by the IPC and in most states (including California, Texas, and Florida), some cities (like parts of New York) restrict or ban AAVs. Always verify with your local authority.
Conclusion
Learning how to plumb a bathroom with sink and toilet only empowers you to add functional space without breaking the bank. With careful planning, the right materials, and attention to code requirements, you can complete this project safely and successfully—even as a beginner.
Remember: Good plumbing isn’t just about pipes—it’s about peace of mind. No leaks, no odors, and no surprise repair bills.
👉 Found this guide helpful? Share it on Pinterest, Facebook, or with a friend tackling their own bathroom project! Your share could save someone hundreds of dollars—and a plumbing headache.
Disclaimer: This article is for informational purposes only. Always comply with local building codes and consult a licensed professional when in doubt.
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