A double bowl kitchen sink is designed to handle two tasks at once, such as washing in one bowl and rinsing in the other. The plumbing underneath looks a little more complex than a single bowl because it must collect wastewater from two drains, keep odors from coming back up, and still maintain smooth flow to your wall drain. With the right parts and a careful step-by-step approach, you can plumb a Double Bowl Sink in a clean, serviceable way that avoids slow drainage and leaks.

What “Double Bowl Sink Plumbing” Includes

Under a typical double bowl sink, each bowl has:

• A sink strainer (or basket strainer) at the drain opening

• A tailpiece dropping down from the strainer

• A continuous waste arm or a second tailpiece to connect both bowls

• A tee or waste kit that merges the two drains

• A P-trap that holds water to block sewer gas

• A trap arm that runs from the P-trap to the wall drain pipe

If you have a dishwasher, you will also have a dishwasher branch tailpiece (a small side inlet) and a hose connection.

Tools and Materials Checklist

Before you start, confirm what type of drain kit you’re installing (most modern sink drain assemblies use slip-joint connections). Gather:

• Adjustable wrench or slip-joint pliers

• Bucket and rags

• Tape measure

• PVC/ABS saw or fine-tooth hacksaw (if you need to cut pipe)

• Deburring tool or sandpaper

• Plumber’s putty or silicone (based on strainer instructions)

• Sink strainer(s) and tailpieces

• Double bowl waste kit (tee + continuous waste arm)

• P-trap kit (matching your pipe size and material)

• Slip-joint nuts and washers (usually included)

A clean installation depends on having the correct sizes. Most kitchen sink drains are commonly 1-1/2 inch, but verify your existing wall drain and trap size before purchasing parts.

Step 1: Shut Off Water and Clear the Cabinet

Turn off the faucet shutoff valves if you will be working around the supply lines, and place a bucket under the existing trap. If you’re replacing old plumbing, loosen the slip-joint nuts, remove the P-trap, and let any trapped water drain into the bucket. Clean the cabinet floor and inspect for damage or mold before reinstalling anything.

Step 2: Install the Sink Strainers Correctly

Each bowl needs a strainer assembly. A properly sealed strainer prevents drips that can look like “mystery leaks” later.

1. Apply plumber’s putty or silicone under the strainer flange as directed by the manufacturer.

2. Seat the strainer in the sink opening and press firmly to spread the sealant.

3. From below, install the gasket(s), backup ring, and locknut.

4. Tighten evenly until snug and stable, then wipe away excess sealant.

If you are using stainless steel sinks, ensure the strainer sits flat and centered. Uneven tightening can twist the gasket and cause slow seepage.

Step 3: Attach Tailpieces and Plan Your Layout

Thread a tailpiece onto each strainer outlet. If one bowl will connect to the trap (often the bowl closer to the wall drain), that tailpiece typically drops straight down into a tee. The second bowl usually connects via a continuous waste arm that slopes slightly toward the tee.

Before tightening everything, dry-fit the parts and check alignment:

• The waste line from the second bowl should flow downhill into the tee.

• The P-trap should sit directly under the tee outlet.

• The trap arm should line up with the wall drain without forcing parts sideways.

A good layout is one that looks relaxed and straight. If you have to “bend” slip joints into position, it will likely leak later.

Step 4: Connect the Two Bowls With a Tee and Continuous Waste Arm

Most double bowl kits merge the bowls using a sanitary tee and an adjustable tubular arm.

• Install the tee on the main bowl tailpiece (or whichever side aligns best with the wall drain).

• Measure the distance from the second bowl tailpiece to the tee inlet.

• Cut the continuous waste arm if needed and deburr the cut edge so washers seal properly.

• Assemble with slip-joint nuts and washers, keeping the arm slightly sloped toward the tee.

Do not overtighten slip-joint nuts. A firm hand-tight plus a small additional turn with pliers is usually enough. Over-tightening can deform washers and create leaks.

Step 5: Add Dishwasher Drain Connection (If Applicable)

If you have a dishwasher, install a dishwasher branch tailpiece on the bowl that makes the most sense for routing the hose cleanly. The hose should rise as high as possible under the countertop (a “high loop”) or connect to an air gap if required by local code.

Secure the dishwasher hose to the branch inlet with a clamp, and ensure the hose routing does not sag downward where water can sit and create odor.

Step 6: Install the P-Trap and Trap Arm to the Wall

Now connect the tee outlet to the P-trap inlet, then connect the trap arm from the P-trap to the wall drain.

Key setup points:

• The P-trap must remain accessible for cleaning.

• The trap arm should run slightly downhill toward the wall drain.

• Avoid creating a second trap or unnecessary bends that can slow drainage.

If the wall drain is too high or too low for the new sink configuration, you may need to adjust the tailpiece lengths or reconfigure the waste kit. The goal is a smooth path: bowl drains into tee, tee into trap, trap into wall.

Recommended Double Bowl Plumbing Layout

A clean under-sink layout typically looks like this:

Step 7: Leak Test and Flow Test

After everything is assembled:

1. Wipe all joints dry.

2. Run water in one bowl for 1–2 minutes, then drain it while watching each joint.

3. Repeat with the other bowl.

4. Fill both bowls halfway and release both drains to stress-test flow.

5. If you have a dishwasher connection, run water and check the branch inlet for seepage.

If you see a slow drip at a slip joint, gently tighten the nut and re-test. If the leak persists, disassemble that joint, verify the washer orientation, and check that the pipe end is smooth and fully seated.

Common Mistakes That Cause Leaks or Slow Draining

• No slope on the continuous waste arm, causing water to sit and drain slowly

• Cross-threaded slip nuts, which never seal reliably

• Rough pipe cuts, which prevent washers from seating

• Overtightened nuts, deforming washers and creating micro-leaks

• Misaligned trap arm, putting sideways pressure on joints

A double bowl sink drains best when both bowls have a clean merge point and the trap sits directly below that outlet.

Choosing a Sink That Makes Plumbing and Maintenance Easier

Plumbing is smoother when the sink is built for consistent drain alignment and durable use. If you’re sourcing sinks for a project or upgrading a kitchen, LANSIDA provides stainless steel kitchen sink solutions that support practical under-sink setups and long-term maintenance. You can explore LANSIDA’s kitchen sink range at gdlansida.com and match bowl configurations, mounting styles, and sink layouts to your cabinet and plumbing plan.

When to Call a Professional

If the wall drain height is incorrect, the drain line is damaged, or local code requires specific venting or air gap rules you can’t meet with your current setup, it’s safer to involve a licensed plumber. But for standard replacements using slip-joint tubular kits, most double bowl sink plumbing can be completed neatly with careful measuring, correct slope, and thorough leak testing.