Yes, you can plumb a double kitchen sink yourself with some basic tools and clear steps. Plumbing a double kitchen sink involves setting up the drains so water flows correctly from both basins into the main waste line, often including a connection for a garbage disposal. This guide will walk you through the entire process, from preparing the area to the final leak check.
Getting Started: Tools and Materials Needed
Before you begin the double kitchen sink drain installation, gather everything you need. Having all parts ready makes the job much smoother.
Essential Tools:
- Pliers (slip-joint or channel-lock)
- Screwdriver set (Phillips and flathead)
- Hacksaw or PVC pipe cutter
- Plumber’s putty
- Bucket and old towels
- Safety glasses
Necessary Materials:
- Basket strainers (two, one for each sink bowl)
- Tailpieces (two)
- Drain fittings (T-connector or continuous waste fitting)
- P-trap assembly (sized for your plumbing rough-in for double sink)
- Trap arm (to connect to the wall drain)
- Pipe dope or Teflon tape (for threaded joints)
- Optional: Garbage disposal unit and its specific connection kit
Step 1: Preparing the Sink and Installing the Baskets
The first main part of plumbing a double basin sink is setting the drain openings for each side.
Placing the Strainer Flange
Each sink bowl needs a drain opening fitted with a basket strainer.
- Clean the Area: Make sure the drain hole in the sink is completely clean and dry. Remove any old putty or debris.
- Apply Plumber’s Putty: Roll a thin rope of plumber’s putty (about 1/4 inch thick). Press this rope all the way around the underside of the strainer flange rim. This putty seals the metal to the sink basin.
- Insert the Flange: Push the strainer flange down firmly into the drain hole from the top side of the sink. Press down hard to squeeze out extra putty around the edge.
- Secure from Below: Go under the sink. Place the rubber gasket, friction ring, and then the large locknut onto the strainer tailpiece threads sticking down.
- Tighten the Locknut: Hand-tighten the locknut first. Then, use your pliers to give it another half to three-quarters of a turn until it is snug. Do not overtighten, as this can crack porcelain or damage composite sinks.
- Wipe Away Excess: From the top of the sink, wipe away all the putty that squeezed out around the flange.
Repeat this process for the second sink bowl.
Step 2: Deciding on the Drain Configuration
How you join the two drains matters a lot for flow. You must decide if you are installing a garbage disposal on one side or using a standard connection for both.
Common Setup A: Connecting Two Standard Drains
If you have no disposal, you need a way to join the two tailpieces before reaching the P-trap. This is usually done with a “T” connector or a continuous waste assembly.
Using a Continuous Waste or Tee:
A continuous waste setup is generally preferred because it ensures good slope and flow, reducing clogs.
- Measure the Space: Look at the space between the two sink bottoms. You need a section that connects the tailpiece from the first sink to the tailpiece of the second sink, leading to the trap arm entrance.
- Assemble the Parts: This assembly typically includes a horizontal pipe section that connects to the lower tailpiece outlet of one sink, runs across, and connects to the lower tailpiece outlet of the second sink.
- Crucial Slope: The pipe linking the two basins must slope downward toward the side where the P-trap will attach. This slope prevents standing water. A good slope is about 1/4 inch drop for every foot of pipe.
Common Setup B: Connecting Garbage Disposal to Double Sink
If one side has a disposal, the plumbing changes slightly. The disposal unit acts as the drain outlet for that side.
- Install the Disposal: Install the garbage disposal unit onto its mounting flange on the sink bowl, following the manufacturer’s specific directions.
- Check Disposal Outlet: The disposal will have a side outlet (usually 1.5 inches). This outlet must connect to the drain line coming from the other sink bowl.
- Connecting to the Other Side: You will use a “T” fitting or a specific dishwasher knockout/inlet piece (depending on the disposal brand) to join the standard drain from the second sink basin to the disposal’s side outlet. This is a key part of connecting garbage disposal to double sink.
Step 3: Installing the Tailpieces and Connecting the Drains
Now we move to the task of connecting double kitchen sink drains beneath the sink.
Double sink drain pipe size is usually 1.5 inches in diameter for residential use. Make sure all replacement pipes match this size.
- Attach Tailpieces: Attach the standard tailpieces to the bottom of the basket strainers. These are the vertical pipes coming straight down from the strainer body. Use pipe dope on the threads if recommended by the manufacturer, and tighten the slip nuts securely.
- Assemble the Linking Pipe: Based on your chosen configuration (Tee or continuous waste), assemble the pieces that run between the two sink drains.
- If using a disposal, the link goes from the standard drain tailpiece to the disposal outlet.
- If no disposal, the link connects the two tailpieces, ensuring it slopes correctly toward the trap entry point. This horizontal run is critical for linking double sink drains effectively.
- Cutting Pipes: You will likely need to cut the connecting pipe sections using your hacksaw or PVC cutter to achieve the right fit and slope. Measure twice, cut once!
- Use Slip Joints: All connections made here use slip nuts and washers. These connections allow for slight adjustments in alignment, which is very helpful when plumbing rough-in for double sink connections aren’t perfectly aligned. Ensure the plastic washers seat correctly inside the fittings before tightening the slip nuts.
Step 4: Installing the P-Trap for Double Sink
The P-trap is vital. It holds a small amount of water to block sewer gases from entering your kitchen. Properly installing P-trap for double sink drainage ensures safety and compliance.
- Determine the Trap Location: The P-trap must connect to the main drain line stubbed out of the wall (the trap arm). The trap inlet should be positioned directly below the lowest point of your newly assembled horizontal drain link.
- Assemble the Trap Components: The P-trap usually consists of a U-bend, a tailpiece extension (if needed), and a trap arm adapter.
- Connecting to the Drain Assembly: Connect the lowest point of your linked drain pipes (the side opposite the disposal, if applicable) to the top inlet of the P-trap assembly. Again, use slip nuts and washers. Make sure the vertical alignment is correct so that the water flows easily into the U-bend.
- Connecting to the Wall Drain: Connect the outlet side of the P-trap (the trap arm) to the drain pipe coming out of the wall. This connection usually requires a slight bend in the trap arm pipe to meet the wall pipe properly. Use an elbow fitting if necessary to create the correct angle toward the wall opening.
A good double sink plumbing diagram shows the P-trap always acting as the lowest point before the pipe enters the wall.
Step 5: Final Checks and Testing
Once all the connections are finger-tight (plus a slight snug from the pliers), it is time to test your work. Leaks are common during the first run.
- Check All Nuts: Go around and gently check every slip nut connection you made—under the strainers, where the two drains meet, and at the P-trap connections. Ensure washers are present and properly seated.
- The Water Test: Place a bucket directly under the P-trap assembly.
- Run Water Slowly: Turn on the hot and cold water in both sink basins, one at a time, then both together. Let the water run for a full minute to ensure all the parts of the double kitchen sink drain assembly are tested under pressure.
- Inspect for Leaks: Watch the pipes closely while the water is running.
- If water drips from a slip nut connection, try tightening that specific nut slightly more. Be careful not to strip the plastic threads.
- If the leak is coming from the strainer basket itself, you may need to tighten the large locknut under the sink or remove the strainer, clean off the old putty, and reapply fresh putty.
- Test Stoppage: Plug both drains and fill one sink partially. Pull the plug and watch the pipes as the water drains quickly. This tests the system under a heavier flow rate.
If everything remains dry after testing, you have successfully completed your double kitchen sink drain installation!
Detailed Component Roles in Double Sink Plumbing
When plumbing a double basin sink, each part plays a specific role in waste removal.
| Component | Primary Function | Material Commonality |
|---|---|---|
| Basket Strainer | Seals the drain hole; holds back large debris. | Metal body, rubber gaskets, putty seal. |
| Tailpiece | Short vertical pipe connecting the strainer to the horizontal drain. | PVC or ABS plastic. |
| Continuous Waste/Tee | Links the two sink drains together before the trap. | PVC or ABS plastic. |
| P-Trap | Holds water seal to block sewer gases. | PVC, ABS, or Chrome-plated metal. |
| Trap Arm | Connects the P-trap to the drain pipe in the wall. | PVC or ABS plastic. |
| Garbage Disposal | Grinds food waste (if installed). | Metal and heavy plastic housing. |
Tips for Smooth Connection Success
Achieving a leak-free system often comes down to small details during the connecting double kitchen sink drains phase.
Maintaining Proper Slope
The biggest enemy of sink drainage is poor slope. Gravity needs to do its job.
- Every horizontal run of pipe—especially the link between the two drains—must slope down toward the P-trap inlet.
- If your plumbing rough-in for double sink is positioned too high or too low relative to the sink drains, you might need to use various lengths of tailpieces or specific offset fittings to maintain that necessary slope.
Working with PVC Joints
PVC and ABS drain pipes connect using friction fittings secured by slip nuts and washers.
- Washers are Key: Always ensure the washer is placed correctly—usually flat against the fitting it is sealing against. A reversed or twisted washer guarantees a leak.
- Don’t Over-Tighten: These are not pressurized water lines. Over-tightening the plastic slip nuts can deform the washer or crack the pipe fitting. Hand-tight plus a small turn with pliers is usually plenty.
Dealing with Garbage Disposal Connections
If you are connecting garbage disposal to double sink, the physical height difference is important.
- Disposals are often taller than a standard tailpiece. You must ensure the drain outlet of the disposal is lower than or equal to the drain outlet of the non-disposal side so that the linking pipe slopes down correctly to the P-trap.
- If the disposal side is too high, you may need a very short tailpiece on the other side or an angled fitting to create the necessary downward pitch for the linked drain assembly.
Frequently Asked Questions About Double Sink Plumbing
What is the standard double sink drain pipe size?
The standard double kitchen sink drain pipe size used in most modern homes for both the strainer tailpieces, the connecting drains, and the P-trap assembly is 1.5 inches in diameter. Older homes might sometimes use 1 1/4 inches, but 1.5 inches provides better flow.
Can I connect both sinks directly to the main waste line without a P-trap?
No, you absolutely must install a P-trap. The water held in the U-bend of the trap prevents foul-smelling sewer gases from rising up through the drain openings and into your kitchen.
How should I connect the two drains if one side has a garbage disposal?
You connect the non-disposal sink drain using a T-fitting or elbow adapter directly to the discharge outlet port located on the side of the garbage disposal unit. The disposal unit acts as one of the primary drains, and the T-fitting links the second basin’s drain into it before heading toward the main P-trap.
What if my pipes don’t line up perfectly for linking double sink drains?
This is common. Drain fittings are designed with slip joints for flexibility. You can often adjust alignment by slightly rotating the fittings or by using various lengths of extension tailpieces or offset elbow fittings to compensate for minor misalignment between the two strainers and the wall pipe. Remember to always maintain the downward slope toward the P-trap.