Skill Level Legend:
Beginner: Simple tools, no flame or cutting involved. Great for first-timers.
Intermediate: Requires basic plumbing knowledge and comfort with hand tools or heat.
Advanced: Complex techniques, potential for damage if done incorrectly. Best left to professionals.
Skill Level:🟡 Intermediate
If you’re planning a kitchen upgrade or replacing old plumbing under your double sink, knowing how to properly plumb it is essential. Done right, you’ll prevent future clogs, backups and headaches. Done wrong, You could be calling in reinforcements sooner than you think, especially if a clogged garbage disposal or partial blockage develops.
So put aside the baking soda and vinegar, by the time you’re done with this article you’ll know how to handle a clogged drain the right way.
Why Plumbing a Double Sink Requires a Bit More Know-How
Unlike a single-basin setup, a double sink has two drain openings that need to flow into the same plumbing system. This can lead to problems like slow draining water, frequent clogs, gurgling noises, or worse foul odors and stagnant water backing up into one side when the other is in use. The key to a trouble-free drainage system is proper alignment, slope, venting and secure connections.
What You’ll Need
Tools:
📌Pipe wrench or channel lock pliers
📌Hacksaw or PVC pipe cutter
📌Tape measure
📌Screwdriver
📌Level
Materials:
📌P-trap kit (1½” diameter)
📌T-fitting (or double waste tee)
📌Extension tubes
📌PVC pipes and elbows
📌PVC primer and cement
📌Plumber’s tape
📌Bucket and towels (just in case!)
Step-by-Step: How to Plumb a Double Sink
1. Shut Off the Water and Prep the Area
While you won’t be dealing with pressurized lines in this job, it’s always good practice to shut off nearby water valves to prevent water leaks. Remove any existing plumbing under the sink and clean the area. Keep a bucket nearby to catch any residual water.
2. Install the Sink Strainers
Insert a strainer into each sink basin to catch any missed food scraps and soap scum that would otherwise create build up. Apply plumber’s putty around the edges to ensure a watertight seal. Secure with lock nuts underneath and wipe away excess putty.
3. Attach Tailpieces
Connect a tailpiece (the straight pipe that drops down from the sink) to each strainer. These will feed into the kitchen sink drain system. Some setups may already include tailpieces; if not, you’ll need to cut them to fit later.
4. Connect the Drains with a Tee Fitting
This is where a double-sink setup diverges from a single drain. Use a T-fitting (or a double waste tee) to connect the two tailpieces together. One arm of the T connects to each tailpiece; the bottom leads to the main drain line. Make sure everything is aligned horizontally and slopes slightly downward toward the main drain about ¼ inch per foot of pipe is ideal to keep food particles and food debris moving, avoid restricting water flow, and prevent buildup that can cause persistent clogs.
5. Install the P-Trap
The P-trap is the curved pipe that traps water to block sewer gases from entering your home. Connect it to the bottom of the T-fitting. Ensure the P-trap aligns properly with the wall or floor drain and adjust if necessary. Use a slip-joint connection so it’s easy to remove later for cleaning or repairs.
6. Connect to the Main Drain
Measure and cut your PVC pipe to connect the P-trap outlet to the existing main waste pipe in the wall or floor. Use PVC primer and cement to create a strong, leak-proof seal. Let it cure as per the product’s instructions.
7. Check Venting
Proper venting is crucial in a double sink. If your home is already vented through the wall (common in most homes), you’re good to go. If not, you may need to install an air admittance valve (AAV) a one-way valve that allows air into the drain to prevent suction and slow draining.
This part may require a permit or be subject to local plumbing codes. When in doubt, consult a licensed plumber, since poor venting can cause more serious problems over time, including pipe damage or a blockage in the system.
This part may require a permit or be subject to local plumbing codes. When in doubt, consult a licensed plumber.
8. Test for Leaks
Run water in both sinks and check every connection for leaks. Tighten slip nuts by hand or with pliers if necessary. If you see dripping or pooling, disassemble, reapply plumber’s tape and reconnect. Run water for at least two minutes in each basin to ensure smooth drainage and no backup.
Common Mistakes to Avoid
📌Wrong slope: If the horizontal pipe between the sinks is level or sloped upward, water won’t drain properly.
📌Too many bends: The more turns you have, the more likely clogs and blockage will form. Keep your design as straight and simple as possible.
📌Over-tightening: PVC and slip nuts don’t need brute force—hand-tight plus a gentle nudge is enough.
📌No venting: This is one of the most overlooked parts of DIY plumbing. Venting prevents gurgling, slow draining, and suction that can empty the trap.
When to Call a Professional Plumber
Even confident DIYers can hit a snag when dealing with hidden venting issues, non-standard pipe sizes, outdated plumbing, or more serious problems. If you’re unsure at any point or just want peace of mind The Great Plumbing Co. is here to help. Our professional plumbers will diagnose the underlying cause and get your double sink plumbed right the first time, saving you time, frustration and costly repairs later.
From Clogged Kitchen Sinks to Leaky Drain Pipes, Trust The Great Plumbing Co.
For nearly three decades, The Great Plumbing Co. has been helping homeowners across Toronto and the GTA keep their plumbing system in top shape. Whether you’re dealing with a leaky hose bib, persistent clogs in sewer lines or a toilet repair, you can trust The Great Plumbing Co. for professional help that delivers timely solutions tailored to your specific requirements.
Regardless of if it’s regular maintenance, kitchen plumbing repair, repiping services or urgent help for plumbing issues, you’ll be glad you called us. Contact us or book online to schedule your residential plumbing appointment.
People Also Ask
Why does my double sink keep backing up?
A double sink usually backs up when both drains share a clogged branch line. Grease, soap residue, and food waste often collect where the two drains meet. If you have a garbage disposal, running cold water during use can reduce buildup, but persistent clogs or standing water in both basins may require a plumber’s snake to clear the blockage.
How should a double sink drain be plumbed?
A double sink should be connected so both bowls meet at a common waste tee before a single P-trap. Proper slope, venting, and secure drain traps are key to prevent backups and ensure water drains freely, which is why it’s usually recommended to seek the help of a professional plumber like The Great Plumbing Co.
How to stop the sink from backing up?
For a clogged sink, start by running hot water to loosen grease, then flush with half a cup of white vinegar to help clear minor clogs. Avoid rinsing food waste, paper towels, or toilet paper into the drain. If backups continue, a drain snake can unclog deeper blockages. Ongoing issues could indicate a more serious problem needing professional repair.
Do you need two P traps for a double sink?
No. A double sink only requires one P-trap. Both bowls connect to a shared drain line before the trap. Two traps can cause siphoning issues, air pockets, and slow draining. Properly connected plumbing with one trap prevents leaks, keeps odors out, and helps maintain a smooth draining process in everyday use.
