How to Hook Plumbing Up to a Double Sink

Upgrading to a double basin sink is one of the most practical improvements you can make to your kitchen, offering ample space for washing dishes and prepping food simultaneously. However, the prospect of connecting the pipes can feel overwhelming for many homeowners who fear leaks or complex configurations. If you are wondering how to hook plumbing up to a double sink, you are in the right place; with the right tools and a bit of patience, this is a very manageable DIY project.

This guide is designed to walk you through the process clearly and safely. We will break down the technical jargon into simple steps, ensuring you understand not just what to do, but why you are doing it. By the end of this article, you will have the confidence to tackle this installation yourself, saving hundreds of dollars in labor costs while ensuring a professional-grade result.

What Tools and Materials Do You Need?

Before you start unscrewing any nuts, preparation is key. Having the right tools on hand prevents mid-project trips to the hardware store, which can kill your momentum. According to general plumbing standards, using high-quality materials significantly reduces the risk of future leaks.

Essential Tools

• Adjustable Wrench or Channel Locks: For tightening slip nuts.
• Screwdriver: Usually flathead or Phillips, depending on your basket strainers.
• Plumber’s Putty or Silicone Caulk: For creating watertight seals around the drain flanges.
• Teflon Tape: For threading connections (if applicable).
• Bucket and Rags: To catch residual water and clean up spills.
• Hacksaw or PVC Cutter: In case you need to trim pipe lengths.

Materials Checklist

• Double Bowl Sink Strainer Kit: Ensure it matches your sink hole sizes (usually 3.5 inches).
• Tailpieces: Two vertical pipes that connect the strainers to the trap.
• Continuous Waste Arm (Tee Fitting): The horizontal piece that connects both drains.
• P-Trap Kit: Includes the curved trap and the wall arm.
• Slip Nuts and Washers: Usually come with the kits, but check for quality rubber gaskets.

Pro Tip: Always buy a “universal” fit kit if you are unsure about your specific pipe diameters. Most modern kitchens use 1.5-inch diameter pipes for sinks.

Step 1: Removing the Old Sink and Plumbing

If you are replacing an existing sink, you must first disconnect the old plumbing. This step is crucial to assess the condition of your current wall pipes and ensure there is no underlying damage.

1. Turn Off the Water: Locate the shut-off valves under the sink and turn them clockwise. Turn on the faucet to release any remaining pressure.
2. Disconnect Supply Lines: Use your wrench to loosen the nuts connecting the water supply lines to the faucet. Have your bucket ready, as some water will drip out.
3. Remove the Old P-Trap: Loosen the slip nuts on the P-trap. Remove the trap and the tailpiece. Inspect the wall pipe (the stub-out) for debris or corrosion.
4. Uninstall the Old Sink: If the sink is clipped in, remove the clips. If it is caulked, use a utility knife to cut the seal. Lift the old sink out carefully.

Clean the area thoroughly. A clean workspace helps you spot potential issues with the countertop or wall pipes before installing the new unit.

Step 2: Installing the New Basket Strainers

The basket strainer is the interface between your sink bowl and the plumbing system. A proper seal here is vital to prevent water from leaking into the cabinet below.

1. Apply Plumber’s Putty: Roll a rope of plumber’s putty about the thickness of a pencil. Place it around the underside of the drain flange (the top part of the strainer).
2. Insert the Strainer: Drop the flange into the drain hole of the sink. Press down firmly so the putty squeezes out evenly.
3. Secure from Below: From underneath the sink, slide the rubber gasket over the threads, followed by the metal locking nut. Hand-tighten the nut, then use your screwdriver or wrench to give it a final quarter-turn.
   • Note: Do not overtighten, as this can crack the sink material or squeeze out all the putty, causing a leak.
4. Clean Up: Wipe away the excess putty that squeezed out around the top of the drain.

Repeat this process for both bowls of the double sink. For more detailed information on drainage systems, you can refer to the general principles of plumbing fixtures on Wikipedia, which outlines standard safety and hygiene requirements.

Step 3: Connecting the Tailpieces and Tee Fitting

This is the core of learning how to hook plumbing up to a double sink. You need to bridge the two separate drains into a single outlet that leads to the P-trap.

1. Attach Tailpieces: Screw the slip nuts and washers onto the bottom of each basket strainer. Insert the tailpieces (vertical pipes) into the strainers. Tighten the nuts by hand, then give a slight turn with pliers.
2. Measure the Distance: Measure the distance between the two tailpieces. You may need to cut the continuous waste arm (the horizontal pipe with a tee in the middle) to fit this width.
3. Install the Tee Fitting: Connect the horizontal waste arm to the two tailpieces. The “tee” section should point downward. This downward outlet is where the P-trap will eventually connect.
   • Alignment Check: Ensure the tee is centered between the two bowls. If one bowl is larger than the other, the tee might be offset, which is perfectly fine as long as the connections are secure.
4. Secure Connections: Tighten all slip nuts. Ensure the rubber washers are seated correctly inside the nuts to prevent leaks.

Step 4: Installing the P-Trap

The P-trap is the U-shaped pipe that holds water, creating a seal that prevents sewer gases from entering your home. It is a critical health and safety component.

1. Connect to the Tee: Attach the top of the P-trap curve to the downward-facing outlet of the tee fitting. Use a slip nut and washer.
2. Connect to the Wall Pipe: Extend the bottom arm of the P-trap toward the wall pipe (stub-out). You may need to adjust the angle or length of this pipe.
   • Cutting Pipes: If the pipe is too long, mark it, cut it with a hacksaw, and deburr the edges.
3. Final Tightening: Connect the wall arm to the stub-out in the wall. Tighten the slip nut. Ensure the P-trap is aligned vertically and not under stress. If it is forced into position, it may crack over time.

Step 5: Testing for Leaks

Never assume the job is done until you have tested it. Water damage can be costly and difficult to repair.

1. Plug the Drains: Put stoppers in both sink basins.
2. Fill with Water: Fill both sides with about 2–3 inches of water.
3. Release the Water: Pull the plugs. Watch the flow. Does it drain smoothly? Is there any gurgling?
4. Check for Drips: While the water is draining and after it has finished, run your hand along all the connections (nuts and joints). Feel for moisture.
5. Tighten if Necessary: If you feel a leak, tighten the corresponding slip nut slightly. If it still leaks, disassemble that joint, check the washer alignment, and reassemble.

Common Mistakes to Avoid

Even experienced DIYers can make mistakes. Here are the most common pitfalls when figuring out how to hook plumbing up to a double sink:

FAQ Section

1. Can I connect a dishwasher to a double sink plumbing setup?

Yes, absolutely. Most double sink setups allow for a dishwasher connection. You typically connect the dishwasher drain hose to the inlet port on the side of the garbage disposal (if installed) or to a dedicated branch tailpiece on the drain line before the P-trap. Ensure you use an air gap or a high-loop installation to prevent backflow.

2. Why is my double sink draining slowly?

Slow drainage is often caused by a clog in the P-trap or the cross-connection between the two bowls. Since food particles can accumulate in the tee fitting, it is a common bottleneck. Try removing the P-trap and cleaning it out. If the problem persists, use a drain snake to clear the wall pipe.

3. Do I need a vent for a double sink?

Yes, every sink drain requires a vent to allow air into the plumbing system, which helps water flow smoothly and prevents siphoning of the P-trap. Typically, a double sink shares a single vent. If you hear gurgling sounds, it might indicate a venting issue, but this is usually related to the main house vent stack, not the under-sink assembly.

4. What is the difference between a P-trap and an S-trap?

A P-trap exits horizontally into the wall, while an S-trap exits vertically into the floor. Modern building codes generally prohibit S-traps because they are prone to siphoning dry, which allows sewer gas to escape. Always use a P-trap for your double sink installation to remain code-compliant.

5. How tight should the slip nuts be?

Slip nuts should be snug but not crushed. A good rule of thumb is to tighten them by hand until they are firm, then use channel locks to turn them an additional 1/4 to 1/2 turn. Overtightening can deform the rubber washer, which actually causes leaks rather than preventing them.

Conclusion

Learning how to hook plumbing up to a double sink is a rewarding skill that empowers you to maintain and upgrade your home independently. By following these steps—preparing your tools, installing strainers correctly, assembling the waste arms, and securing the P-trap—you ensure a leak-free and efficient drainage system. Remember, the key to success lies in patience, proper alignment, and thorough testing.

Now that you have mastered this installation, why not share this guide with a friend who is planning a kitchen renovation? Or, pin this article to your Pinterest board for future reference. Happy plumbing!