How To Plumb Double Kitchen Sink: Easy Steps

Yes, you can absolutely plumb a double kitchen sink yourself by following a few clear steps. Plumbing a double kitchen sink involves connecting two separate drain openings into one main drain line, usually with a special setup called a sanitary tee. This double sink plumbing guide will show you how to do it safely and correctly, whether you are installing double bowl kitchen sink for the first time or replacing old pipes.

Tools and Materials Needed for the Job

Before you start connecting double kitchen sink drains, gather everything you need. Having the right tools makes the job much faster and cleaner.

Tool Category	Specific Items	Purpose
Measuring & Cutting	Tape Measure, Hacksaw or PVC Pipe Cutter	For sizing pipes correctly.
Joining Pipes	PVC Primer and Cement (for plastic) or Flux and Solder (for metal)	To create leak-proof seals.
Assembly	Slip-joint Pliers or Basin Wrench	To tighten tricky nuts under the sink.
Sealing	Plumber’s Putty or Silicone Caulk	To seal the sink drain flanges.
Safety	Safety Glasses, Work Gloves	To protect your eyes and hands.

Materials Checklist:

Sink Strainers/Flanges: Two sets, one for each bowl.
Tailpieces: Short pipes connecting the strainer to the main drain assembly.
Center Tee or Sanitary Tee: The crucial piece for connecting two sink drains.
P-Trap Assembly: The curved pipe that stops sewer gas from entering your home. This is key for the kitchen sink P-trap double sink.
Horizontal Drain Pipe: To connect the P-trap to the wall drain.
Disposal Connection Parts (if applicable): For garbage disposal double sink installation.

Step 1: Preparing the Sink and Installing the Strainers

The first major step in installing double bowl kitchen sink is setting up the drain openings in the sink bowls themselves.

Applying Plumber’s Putty

Each sink bowl needs a drain strainer installed. This piece seals the drain hole against the sink basin.

Clean the Area: Make sure the sink drain opening is totally clean and dry.
Roll the Putty: Take a small amount of plumber’s putty. Roll it into a thin rope, about 1/4 inch thick.
Apply the Seal: Wrap this putty rope all the way around the underside rim of the sink strainer flange (the part that sits inside the sink bowl).
Set the Strainer: Push the strainer firmly down into the sink drain hole from above. Press hard to squeeze out extra putty.

Securing the Strainer from Below

From under the sink, you will see the threaded part of the strainer sticking down.

Add the Washer: Slide the rubber gasket (washer) onto the threaded tailpiece underneath the sink.
Attach the Locknut: Screw the large metal locknut onto the strainer threads.
Tighten Firmly: Use your slip-joint pliers or basin wrench to tighten the locknut. Tighten it until the putty squeezes out evenly around the top edge inside the sink.
Clean Up: Scrape away all the excess putty that squeezed out from around the strainer edge inside the sink basin.

Repeat this for the second sink bowl. Now you have two separate drain outlets ready for the next phase of connecting double kitchen sink drains.

Step 2: Setting Up the Drain Lines and the Center Tee

This is where we bring the two drains together. The goal is to route both tailpieces to a central connection point.

Attaching Tailpieces

A tailpiece is a short pipe section. You attach one to the bottom of each sink strainer.

If you are using a sink drain assembly double bowl kit, the tailpieces should be the correct length or adjustable.
If the strainer already has a short pipe attached, skip this or adjust its height.

Choosing the Right Connection Piece

You have two main options for joining the two drain lines:

The Center Tee (or Wye Fitting): This is used when you have one side that drains lower than the other (common with garbage disposals).
The Sanitary Tee: This fitting is used when the two drains are mostly level. It has three openings—one for each sink and one pointing down to the P-trap. This is essential for proper flow.

For a standard setup without a disposal, you will use a sanitary tee.

Connecting the Drains with the Sanitary Tee

Measure and Cut: Hold the sanitary tee between the two tailpieces coming off the sink strainers. Measure the space required for the straight sections of pipe (the horizontal run). Cut your PVC pipe pieces to fit this span, allowing a slight slope toward the center tee.
Dry Fit Everything: Before gluing anything, assemble the entire structure: Tailpiece A $\rightarrow$ Pipe $\rightarrow$ Sanitary Tee $\rightarrow$ Pipe $\rightarrow$ Tailpiece B. Make sure it lines up well with where your main drain pipe enters the wall.
Cementing the Joints (If using PVC): Take the assembly apart piece by piece. Clean the ends of all pipes and the inside sockets of the fittings. Apply PVC primer to both surfaces. Then, apply PVC cement to both surfaces and quickly push the pipe and fitting together, giving it a quarter turn to spread the cement. Hold firmly for 30 seconds.
Assemble the Run: Connect the tailpieces to the center tee using the newly cemented short pipes. This forms the top part of your plumbing diagram double kitchen sink.

Step 3: Installing the P-Trap

The P-trap is not just for looks; it is a crucial safety device. It holds a small amount of water to block sewer gases from coming up through your drain.

What is the Kitchen Sink P-Trap Double Sink Setup?

For a double sink, the main drain line must connect to the trap assembly correctly.

Connect the Trap Arm: The P-trap needs a pipe section leading out of it, called the trap arm, which goes into the wall drain stub.
Positioning: The bottom curve of the P-trap must be lower than the inlet from the sanitary tee. This gravity flow ensures water moves out, but a small water seal remains in the trap curve.
Assembling the Trap: Use the slip-joint connections (the large nuts that slide over the pipe) to assemble the curved U-bend and the straight pieces leading to and from the sanitary tee. Do not overtighten these yet. You need them slightly loose for final adjustments.

Finalizing the Connection to the Wall

The outlet pipe from the P-trap must align with the existing drain pipe coming out of the wall (or floor).

If the alignment is perfect, you can use a small piece of pipe and fittings to connect it.
If the wall pipe is higher or lower than the trap outlet, you may need to adjust the height of the entire assembly, often by shortening or lengthening the tailpieces or using an offset in the connection pipe.

Step 4: Plumbing for a Garbage Disposal Double Sink Installation

If one side of your sink has a garbage disposal double sink installation, the process changes slightly. The disposal unit replaces the standard strainer and tailpiece on that side.

Integrating the Disposal Unit

The disposal unit acts as the drain outlet for one bowl.

Install the Disposal Mount: Follow the manufacturer’s instructions to attach the mounting ring for the garbage disposal to the sink flange on the side designated for the disposal. This mount is typically secured with screws or a snap ring underneath.
Connecting the Disposal: Mount the disposal unit onto its mounting ring.
The Dishwasher Connection: If you have a dishwasher, this is the time to handle the dishwasher connection double sink drain line. The dishwasher hose usually connects to a small nipple (port) molded into the side of the garbage disposal housing. If you don’t use a dishwasher, plug this port securely with the provided knockout plug or cap.
Knocking Out the Plug (Crucial Step!): If you plan to connect a dishwasher or the second sink drain to the disposal, you must knock out the plug inside that inlet port on the disposal unit. Use a screwdriver and a hammer to tap the plug inward, then retrieve the plastic piece from inside the disposal chamber before assembly is complete.

How to Plumb a Double Sink Disposal Setup (Two Disposals)

If you have a disposal in both sinks, you will need two disposal units.

Each disposal has an outlet port near the bottom.
You connect these two outlets using a specialized Y-fitting or two short pipes leading into a single, larger pipe that then connects to the main drain line.
This often requires a custom plumbing diagram double kitchen sink approach, as the two units are usually close together.

Connecting One Disposal to the Second Sink

This is the most common setup.

The disposal outlet replaces the tailpiece for the first sink.
The second sink (the regular drain) connects to the disposal via a side inlet, often using a specialized fitting that directs flow from the second strainer into the side of the disposal chamber. This requires careful alignment.

Step 5: Finalizing Connections and Testing for Leaks

Once all the pipes, tees, and traps are assembled, it’s time to ensure everything is tight and leak-proof.

Tightening Slip Joints

Go back to all the large nuts on the P-trap and the connections leading into the sanitary tee.

Hand-tighten them first.
Use pliers for just another quarter turn. Be careful not to crush plastic fittings. If you use metal fittings, a wrench is fine, but stop as soon as you feel firm resistance. Overtightening plastic causes cracks later.

The Test Run

Plug the Second Sink: If you only have one sink draining right now (like testing the disposal side), plug the other sink drain opening completely using the stopper.
Run Water Slowly: Turn on the faucet for the bowl you are testing. Start with a slow stream. Watch all the connections underneath carefully for drips.
Increase Flow: After a minute with no drips, run the water at full blast for a minute or two.
Check Every Joint: Pay special attention to the joints where the putty was used (the strainers) and all the slip-joint connections on the P-trap.
Test Both Sides: If you tested the disposal side, repeat the process for the second, standard drain side.

If you see a drip, gently tighten that specific slip-joint nut slightly more. If the leak persists, you might need to disassemble that joint, check the rubber washer inside, and reassemble.

Deciphering Pipe Slopes and Gravity Flow

For your plumbing to work well, water must move downhill toward the main drain in the wall. This concept is vital for the kitchen sink P-trap double sink assembly.

Horizontal Pipe Slope Requirements

The Rule: Any horizontal pipe carrying wastewater must slope downward toward the main sewer line or stack.
The Measurement: Aim for a drop of about 1/4 inch for every foot of pipe run. This ensures solids are carried away by the water and don’t build up.
In Practice: When connecting two sink drains with a center tee, ensure the piping between the sink tailpieces and the tee slopes slightly toward the tee. The P-trap arm leading to the wall should also slope down toward the wall.

If your pipes run too flat, you get slow drains and clogs. If the slope is too steep, the water rushes out too fast, leaving solids behind.

Garbage Disposal Maintenance Considerations

If you installed a disposal, remember these extra points specific to how to plumb a double sink disposal:

Air Gap vs. Air Admittance Valve (AAV): Depending on local codes, your dishwasher drain might need an air gap device installed on the countertop, or you might be allowed to use an AAV if the main drain is vented improperly. Check local rules.
The Knockout Plug Revisited: Never run the dishwasher or the second sink drain if the knockout plug inside the disposal inlet is still in place. This is the single most common mistake in garbage disposal double sink installation.

Components Detail: The Anatomy of the Double Sink Drain

To truly master connecting double kitchen sink drains, it helps to know the names of the main parts in the plumbing diagram double kitchen sink:

Component Name	Function	Importance
Flange/Strainer	Sits in the sink hole, sealed with putty.	Prevents leaks at the sink surface.
Tailpiece	Short pipe connecting the strainer to the tee fitting.	Sets the height of the assembly.
Sanitary Tee	Fitting that combines the two drain lines.	Ensures smooth flow into the trap.
P-Trap	The U-shaped bend in the pipe.	Blocks sewer gas from entering the kitchen.
Trap Arm	Pipe leading from the P-trap into the wall/main stack.	Must maintain a downward slope.

Frequently Asked Questions About Double Sink Plumbing

Q: Can I connect both sink drains directly to the wall pipe without a P-trap?

A: No. You must install a P-trap on the combined drain line. Without a P-trap, sewer gases carrying bad smells and potentially dangerous bacteria will rise directly into your kitchen through the drain opening. The trap holds standing water to prevent this.

Q: What size pipe should I use for a double kitchen sink?

A: Standard kitchen drains use 1 1/2 inch (1.5″) diameter pipe for the entire assembly, including the tailpieces, tee, and P-trap. The drain pipe entering the wall should also typically be 1.5 inches, though some larger homes might use 2-inch pipe.

Q: How high should the P-trap be off the floor?

A: This depends on where the main drain line in the wall is located relative to your sink cabinet. Generally, the P-trap inlet (where the water comes from the sink) should be higher than the trap outlet (where it goes into the wall). The bottom of the trap loop should sit just above the height of the horizontal pipe entering the wall, allowing gravity to move the water out smoothly. Always check local plumbing codes for exact height requirements relative to the floor drain.

Q: I have slow draining. What is the first thing to check in my double sink plumbing?

A: First, check the slope of the horizontal pipes, especially the connection between the two drains and the trap arm going to the wall. If the pipes are too flat, debris builds up. Second, check the P-trap itself for blockage. If you have a disposal, ensure the knockout plug wasn’t left in if you connected another drain to it.

Q: Do I need plumber’s putty or silicone caulk for the sink strainer?

A: Plumber’s putty is the traditional and generally preferred material for sink strainers because it remains pliable and allows you to easily remove the strainer later for cleaning or repairs. Silicone caulk creates a very hard seal, making future removal much more difficult. Use putty unless the sink material (like certain types of granite composite) specifically calls for silicone.