How To Plumb A Double Kitchen Sink: DIY Guide

by

Can you plumb a double kitchen sink yourself? Yes, with the right tools and a bit of patience, most homeowners can tackle plumbing a double kitchen sink. This guide will walk you through the process, from understanding the parts to making the final connections. We’ll cover double bowl sink plumbing essentials, how to get your sink trap installation correct, and the best way to manage connecting kitchen sink drains.

A double kitchen sink offers more workspace, making tasks like washing dishes and preparing food easier. Properly plumbing it ensures efficient drainage and prevents leaks. This guide focuses on standard kitchen sink setups, typically using PVC pipes.

Tools and Materials You’ll Need

Before you start, gather all your tools and materials. Having everything on hand will make the job smoother.

Essential Tools:

  • Adjustable Wrench: For tightening and loosening fittings.
  • Pipe Wrench: For gripping and turning pipes.
  • Plumber’s Putty or Silicone Caulk: For sealing around the drain openings.
  • Hacksaw or PVC Pipe Cutter: To cut pipes to the correct length.
  • Measuring Tape: For accurate measurements.
  • Bucket: To catch any residual water.
  • Safety Glasses: To protect your eyes.
  • Gloves: To keep your hands clean.
  • Drop Cloth: To protect your cabinet floor.
  • Screwdriver: For various fittings.
  • Level: To ensure proper drainpipe slope.

Key Materials:

  • Double Sink Drain Assembly: This usually includes the strainer basket, tailpiece, and flange for each sink bowl.
  • Sink Trap (P-trap): You’ll need a P-trap kit designed for a double sink. This often involves a special tee fitting. A P trap for double sink is crucial for preventing sewer gases from entering your home.
  • Tailpieces: Short sections of pipe that connect the sink drain to the trap.
  • Couplings and Connectors: Various PVC fittings like elbows, tees, and unions for joining pipes.
  • PVC Cement and Primer: For creating strong, leak-proof bonds between PVC pipes and fittings.
  • Thread Seal Tape (Teflon Tape): For threaded connections.
  • Sink Overflow Piping (if applicable): Some sinks have overflow holes that need to be connected.
  • Dishwasher Drain Hose: For connecting your dishwasher.
  • Garbage Disposal Flange and Adapter (if installing a disposal): This is a special part that connects your disposal to the sink drain. Garbage disposal plumbing has its own set of considerations.
  • Main Drainpipe: The larger pipe that carries waste away from your sink. Ensure you have the correct diameter, often a 1.5-inch or 2-inch PVC kitchen drain pipe.

Step-by-Step Guide to Plumbing Your Double Kitchen Sink

Let’s break down the process into manageable steps.

Step 1: Preparing the Sink and Cabinet

  1. Clear the Area: Remove everything from under your sink. Lay down a drop cloth to protect the cabinet floor from water and debris.
  2. Inspect Existing Plumbing: Look at how the current drain system is set up. Note the location of the main drainpipe and any existing trap.
  3. Clean Drain Openings: Ensure the drain openings in your sink are clean and free of any old putty or sealant.

Step 2: Installing the Sink Drain Assemblies

This is the first major step in double bowl sink plumbing.

  1. Apply Plumber’s Putty/Caulk: Roll a snake of plumber’s putty into a rope about 1/2 inch thick. Place this rope around the underside of the sink drain flange for each sink bowl. Alternatively, use a thin bead of silicone caulk.
  2. Insert the Flange: Push the drain flange down into the sink drain opening from the top.
  3. Add Gasket and Washer: From underneath the sink, slide the rubber gasket onto the drain flange, followed by the friction washer (often made of cardboard or fiber).
  4. Tighten the Locknut: Screw the locknut onto the threaded portion of the drain flange. Tighten it firmly with an adjustable wrench. You don’t need to overtighten, but it should be snug enough to compress the gasket and create a watertight seal.
  5. Wipe Away Excess: From inside the sink, wipe away any excess plumber’s putty or caulk that squeezed out around the flange.
  6. Repeat for the Second Bowl: Do the same for the other sink bowl.

Your sink drain assembly is now in place for both bowls.

Step 3: Connecting the Sink Traps (The Core of Double Sink Plumbing)

This is where double bowl sink plumbing gets a bit more complex than a single sink. The goal is to efficiently move water from both sinks to the main drain.

Understanding the Double Sink Trap Setup

A common method for a double sink involves a special “double bowl sink waste kit” or using a specific tee fitting. The idea is to have a central trap that serves both sinks.

  1. Assemble the Trap Components: Your kit will likely include two tailpieces, a tee fitting, and a P-trap. One tailpiece connects to the bottom of the strainer assembly of one sink bowl, and the other tailpiece connects to the second sink bowl.
  2. Connecting Tailpieces to Strainers:
    • Slip a rubber gasket onto the bottom of each sink drain flange.
    • Slide a tailpiece onto the threaded outlet of the sink drain assembly.
    • Secure the tailpiece with a slip nut and washer. Tighten snugly with a wrench.
  3. Connecting to the Tee Fitting:
    • The tee fitting will have one inlet for each tailpiece and one outlet that connects to the P-trap and then the main drain.
    • Slide slip nuts and washers onto the ends of the tailpieces coming from the sink bowls.
    • Insert the tailpieces into the side inlets of the tee fitting. Tighten the slip nuts.
    • Ensure the tee fitting is oriented correctly so that the outlet for the P-trap is facing the main drainpipe.
  4. Installing the P-Trap:
    • Connect the P-trap to the outlet of the tee fitting. The P-trap’s shape is essential for holding water, which creates a seal against sewer gases. This is why a sink trap installation is so vital.
    • Attach the P-trap to the tee using slip nuts and washers.
    • Connect the outlet of the P-trap to the main drainpipe. You might need an adapter or a piece of pipe to bridge the gap, ensuring you maintain the correct drainpipe slope.

Important Note on Drainpipe Slope

For proper drainage, the horizontal drainpipes should slope downwards towards the main drain. A slope of 1/4 inch per foot is standard for PVC kitchen drain pipes. Use a level to check this as you connect your pipes. Incorrect slope can lead to clogs and slow draining.

Step 4: Connecting to the Main Drain

  1. Measure and Cut: Measure the distance from the outlet of your P-trap to the main drain connection point. Cut a piece of PVC pipe to the correct length.
  2. Dry Fit: Before cementing, dry-fit all the pieces to ensure they align correctly and the slope is maintained.
  3. Prepare for Cementing: Clean the ends of the pipes and fittings with a primer. This cleans and softens the PVC for a better bond.
  4. Apply PVC Cement: Apply PVC cement to both the pipe end and the inside of the fitting. Work quickly, as the cement dries fast.
  5. Join Pipes: Push the pipe into the fitting with a slight twist to spread the cement evenly. Hold for about 30 seconds to allow the cement to set.
  6. Check Slope Again: Use your level to confirm the correct drainpipe slope on this final connection.

Step 5: Installing the Garbage Disposal (If Applicable)

If you’re installing a garbage disposal, garbage disposal plumbing needs to be integrated into the system.

  1. Mount the Disposal: Follow the manufacturer’s instructions to mount the garbage disposal to the larger flange on one of the sink bowls. This usually involves a mounting ring and screws.
  2. Connect Disposal Outlet: The disposal will have an outlet that needs to connect to the drain system.
    • Option 1: Direct Connection to Tee: Some setups allow you to connect the disposal directly to a specific inlet on the tee fitting used in double bowl sink plumbing.
    • Option 2: Via Tailpiece: You might need an adapter to connect the disposal’s outlet to a tailpiece, which then connects to the tee.
  3. Knockout Plug: If you’re connecting a dishwasher to the disposal, you must remove the knockout plug inside the disposal’s dishwasher inlet. If you are not connecting a dishwasher, ensure the plug remains firmly in place.
  4. Secure Connections: Use slip nuts and washers to secure the disposal connection to the drain pipes.

Step 6: Connecting the Dishwasher Drain

The dishwasher drain hose typically connects to the disposal or directly to the sink drain system.

  1. Locate Connection Point:
    • Disposal: If you’re using a garbage disposal, connect the dishwasher drain hose to the dedicated inlet on the disposal (remember to knock out the plug first if applicable).
    • Drainpipe: If not using a disposal or if the disposal has no inlet, you might need a special dishwasher tailpiece that has a side inlet for the hose.
  2. Secure Hose: Clamp the dishwasher drain hose securely to the disposal inlet or the tailpiece fitting to prevent leaks. Ensure the hose has a “high loop” (secured to the underside of the countertop) to prevent dirty water from flowing back into the dishwasher.

Step 7: Installing Sink Overflow Piping (If Applicable)

Some sinks have overflow holes designed to prevent flooding.

  1. Attach Overflow Tube: If your sink has overflow holes, there will be a small pipe or tube that connects to them. Attach this overflow pipe to the back of the sink or the overflow opening.
  2. Connect to Drain: This overflow pipe typically connects to one of the tailpieces or the tee fitting in the drain assembly using a small threaded connection and gasket. This is the sink overflow piping.

Step 8: Testing for Leaks

This is a crucial step after connecting kitchen sink drains.

  1. Fill the Sinks: Fill both sink bowls with water, one at a time, to about half full.
  2. Check All Connections: While the water is in the sinks, inspect every joint, fitting, and connection point for any signs of dripping or leaks. Pay close attention to:
    • The underside of the sink drain flanges.
    • All slip nuts and washers.
    • The tee fitting.
    • The P-trap connections.
    • Where the P-trap connects to the main drain.
    • Any connections related to the garbage disposal or dishwasher.
  3. Drain the Sinks: Once you’ve checked for leaks with the sinks full, allow them to drain. Watch the pipes as the water flows to identify any leaks that only occur during draining.
  4. Tighten if Necessary: If you find any leaks, turn off the water supply (if applicable) and gently tighten the loose fitting. Avoid overtightening, which can crack PVC or strip threads. Sometimes, disassembling and reassembling the connection with new plumber’s putty or tape is necessary.

Step 9: Final Touches

  1. Clean Up: Remove all tools, materials, and the drop cloth.
  2. Organize Cabinet: Place your cleaning supplies and other items back under the sink.

Common Issues and Troubleshooting

Even with careful work, you might encounter a few problems.

Slow Draining

  • Cause: Improper drainpipe slope, partial clogs in the pipes, or debris in the trap.
  • Fix: Ensure the slope is correct (1/4 inch per foot). Check the P-trap for blockages and clean it out. Run hot water and a bit of baking soda and vinegar to help clear minor clogs. If issues persist, you may have a clog further down the line.

Leaks at Slip Joints

  • Cause: Loose slip nuts, worn-out washers, or improper seating of the washer.
  • Fix: Tighten the slip nut. If it continues to leak, disassemble the joint, inspect the washer (replace if damaged), and reassemble, ensuring the washer is correctly seated.

Sewer Gas Odors

  • Cause: The water seal in the P-trap has evaporated or been siphoned out, allowing sewer gases to enter. This can happen if a sink isn’t used regularly or if there’s a blockage that causes siphoning.
  • Fix: Run water in the sink for a minute to refill the trap. If the issue is frequent, ensure your sink trap installation is correct and there are no venting problems in your plumbing system.

Garbage Disposal Not Draining Properly

  • Cause: Clogs within the disposal unit or its connecting pipes.
  • Fix: Turn off the power to the disposal at the breaker. Use a flashlight to look inside the disposal for obvious blockages and remove them with pliers (never put your hand inside). Check the P-trap and pipes connected to the disposal for clogs.

Frequently Asked Questions (FAQ)

Q1: Do I need a special kit for a double sink?

A1: While you can assemble the necessary parts individually, a “double bowl sink waste kit” often simplifies the process by providing the correct tee fitting and tailored tailpieces for double bowl sink plumbing.

Q2: What is the correct slope for a PVC kitchen drain?

A2: The standard drainpipe slope for a PVC kitchen drain is 1/4 inch per foot of horizontal pipe length. This ensures water and waste flow away efficiently.

Q3: Can I connect a garbage disposal to only one side of a double sink?

A3: Yes, it’s common to install a garbage disposal on one side and use the other side for manual washing or rinsing. You’ll need to ensure the disposal’s plumbing is correctly integrated into the double bowl sink plumbing.

Q4: How do I prevent sewer gases from coming up through my double sink?

A4: A proper sink trap installation is the primary defense. The U-shaped P-trap holds water, creating a seal. Ensure the trap is correctly installed and never allowed to dry out.

Q5: What materials should I use for connecting kitchen sink drains?

A5: For most modern kitchen sinks, PVC kitchen drain pipes and fittings are standard due to their durability and ease of use. You’ll also need plumber’s putty or silicone caulk for sealing, and PVC cement and primer for permanent bonds.

By following these steps, you can successfully plumb your double kitchen sink, ensuring efficient and reliable drainage. Remember to prioritize safety and double-check all connections for leaks.