Plumbing a kitchen sink involves several key steps, from installing the drain assembly to connecting the water lines. If you are asking, “What is the basic process for plumbing a kitchen sink?” the answer is generally: first, install the drain components like the basket strainer and disposal (if applicable), then connect these drains using the P-trap to the main waste line, and finally, connect the hot and cold water supply lines to the faucet. This guide will walk you through the entire process simply and clearly.
Preparing for Your Kitchen Sink Plumbing Project
Before you start fitting pipes, you need the right tools and parts. Good preparation saves a lot of time and frustration later.
Essential Tools and Materials Checklist
Gather everything you need before turning off the water supply. Having things ready makes the job run smoothly.
- For the Drain: Pipe wrench, plumber’s putty, screwdriver, adjustable wrench, plastic pipe sections (for the P-trap), new basket strainer(s).
- For the Water Lines: Adjustable wrenches, supply line hoses (flexible braided lines are best), Teflon tape (pipe thread sealant tape).
- Safety Gear: Safety glasses and gloves.
- Optional (but helpful): Bucket, towels, flashlight, hacksaw (if cutting drain pipes).
Getting the Right Measurements
Knowing your sink rough-in measurements is vital. These measurements tell you where the drain opening and water lines are located relative to the cabinet floor and back wall.
- The drain pipe (the tailpiece) coming down from the sink usually needs to align with the existing drain in the wall or floor.
- Most standard sinks require the drain connection point to be roughly 15 to 20 inches below the sink basin. Check local codes for exact height requirements for the trap weir.
Step 1: Installing the Kitchen Sink Basket Strainer
The basket strainer is the metal piece that fits into the sink hole and holds the drain plug. This is a crucial part of your kitchen sink drain installation.
Applying Plumber’s Putty
Plumber’s putty creates a watertight seal under the strainer flange. Do not use silicone caulk unless the strainer specifically calls for it, as putty is easier to remove later.
- Take a small rope of plumber’s putty. Make it about the thickness of a pencil.
- Wrap this putty ring completely around the underside edge of the strainer flange.
Securing the Strainer to the Sink
This process can differ slightly between single and double sinks, but the method is mostly the same for each drain opening. For a plumbing double bowl sink, you repeat this for both sides.
- Push the strainer flange down firmly into the sink drain hole. Wipe away any putty that squeezes out inside the sink basin.
- From underneath the sink, slide the friction washer (usually rubber or plastic) up over the tailpiece threads.
- Screw the large locknut onto the tailpiece threads from below.
- Use a large wrench or pliers to tighten this locknut firmly. Do not overtighten, or you might crack a porcelain sink. The goal is a firm seal.
- Wipe away any remaining excess putty from the top of the sink.
Connecting Garbage Disposal to Sink (If Applicable)
If you are connecting garbage disposal to sink, this happens right after the strainer is installed.
- Mount the mounting ring assembly (which came with the disposal) onto the tailpiece extending from the new basket strainer.
- Secure the disposal unit to this mounting ring using the locking ring provided. This usually requires turning the disposal slightly until it locks firmly into place.
- Make sure the disposal inlet opening lines up correctly with the other drain pipe that will connect to the P-trap.
Step 2: Mounting the Kitchen Sink Faucet
Before you put the sink in place (if it’s a new installation) or simply work underneath, you need to attach the faucet. This involves mounting kitchen sink faucet hardware.
Faucet Base Plate and Gaskets
Most modern faucets come with a base plate or escutcheon to cover extra holes in older sinks.
- Feed the faucet supply lines and mounting shanks down through the holes in the sink deck.
- From below, slide the necessary gaskets and the mounting bracket onto the shanks.
- Hand-tighten the mounting nuts onto the shanks.
- Use a basin wrench or adjustable wrench to securely tighten these nuts. Ensure the faucet is perfectly straight before final tightening.
Connecting Sink Water Lines
Now it is time for connecting sink water lines. These lines bring hot and cold water up to the faucet.
- Identify the hot (usually red or marked ‘H’) and cold (usually blue or marked ‘C’) supply lines coming from your faucet tailpieces.
- Connect these lines to the corresponding shut-off valves coming out of the wall or floor under the sink.
- Use flexible braided supply lines for this connection. They make fitting easier than rigid pipes.
- Tighten the connections at the valves using an adjustable wrench. Tighten them firmly, but stop once you feel resistance to avoid stripping the threads.
Step 3: Assembling the Drain Piping and P-Trap
This is the core of your plumbing work. You are connecting the sink drain assembly to the waste line stub-out using traps and fittings. Reviewing an under sink plumbing diagram helps ensure correct alignment.
The Role of the P-Trap
The P-trap is essential. Its curved shape holds a small amount of water, creating a seal that stops sewer gases from rising up the drainpipe and into your kitchen. Knowing how to install a sink P-trap correctly is vital for safety and odor control.
Tailpieces and Fittings
You will likely need several pieces of pipe (tailpieces) to connect the strainer assembly to the P-trap inlet.
- Measure the distance between the bottom of the sink strainer (or the garbage disposal outlet) and the inlet of the P-trap.
- Cut the straight plastic tailpiece pipes to the necessary length. You want as few elbows as possible, ideally just the necessary trap bend.
- Assemble the pieces using slip-joint washers and slip nuts. These fittings are designed to be hand-tightened, then given a quarter to a half turn with pliers for a good seal.
Connecting the Waste Line
The final connection joins the P-trap outlet arm to the main drain pipe coming out of the wall or floor.
- The outlet arm of the P-trap must align with the stub-out drain pipe. If they don’t line up perfectly, you might need an angled elbow or a short section of pipe to bridge the gap.
- Ensure the entire drain assembly slopes slightly downward toward the main drain. Gravity does the rest of the work.
- When connecting the drain arm to the wall pipe, use a larger slip joint connection, ensuring the washer is seated correctly.
Step 4: Final Checks and Testing the Plumbing
Never skip the testing phase. Even if everything looks tight, water pressure reveals weak spots immediately.
Checking Water Supply Connections
- Slowly turn on the hot and cold water shut-off valves under the sink. Listen for any immediate spraying sounds.
- Run the faucet at a low flow for a minute, checking all connections between the faucet and the shut-off valves. Look for drips. Tighten slightly if needed.
Testing the Drain System
Testing the drain requires running a large volume of water quickly.
- Plug the sink drain(s). Fill the sink basin(s) halfway with water.
- Quickly pull the plug and let all the water rush down the drain at once.
- Immediately get under the sink with a dry paper towel or flashlight. Watch every connection point in the drain line—strainer nut, disposal mount, P-trap connections, and the connection to the wall pipe.
- If you see a slow drip, try gently tightening the corresponding slip nut. If tightening does not work, you must disassemble that joint, check the washer, and reassemble it.
Follow these sink drain assembly instructions carefully to avoid leaks.
Special Considerations: Plumbing Double Bowl Sink
When dealing with a plumbing double bowl sink, the challenge is merging the two separate drains into one waste line before the P-trap.
Center Outlet vs. End Outlet Bins
Sinks are designed either for the drain assemblies to meet in the center or at one side. You must use the correct fittings to connect the two strainer tailpieces.
- You will typically use a continuous waste fitting, which is a pipe with two inlets. This piece connects the tailpiece of the strainer that does not have the garbage disposal attached.
- If you have two strainers and one garbage disposal, one strainer connects directly to the disposal flange, and the other connects to the disposal inlet via a continuous waste pipe.
- The outlet arm from the continuous waste fitting or the disposal connects directly to the P-trap inlet.
This configuration ensures that water from both sides flows into the trap correctly. The under sink plumbing diagram for a double sink will clearly show this tee or continuous waste piece.
Deciphering Plumbing Codes and Best Practices
While this guide covers the physical steps, local plumbing codes dictate specifics like trap height and material usage.
Why Pipe Sealant Matters
When joining threaded connections (like the tailpiece nuts), always use plumber’s putty or pipe dope (thread sealant) as specified for the fittings involved. For PVC or ABS plastic drain pipes, solvent cement is used for permanent joints, while slip nuts use gaskets for disassembly.
Pipe Material Selection
Most modern kitchen sink drains use PVC (white plastic) or ABS (black plastic). Ensure all fittings you buy match the material already installed in your home’s waste lines.
Table 1: Common Plumbing Component Functions
| Component | Primary Function | Connection Type |
|---|---|---|
| Basket Strainer | Seals the sink opening; holds back large debris. | Plumber’s Putty/Locknut |
| Tailpiece | Straight pipe section leading down from the strainer. | Slip Joint Washers |
| P-Trap | Holds water to block sewer gas. | Slip Joint Washers |
| Shut-off Valve | Controls water flow to the faucet. | Threaded Connection |
Frequently Asked Questions (FAQ)
What is the required diameter for kitchen sink drain pipes?
Standard kitchen sink drains use a 1 1/2-inch diameter pipe for the tailpieces and P-trap. The main drain line in the wall is usually 1 1/2 inches or 2 inches, depending on local code and if a garbage disposal is present (disposals often mandate 2-inch lines).
Can I use glue instead of compression fittings for the P-trap?
For plastic drain pipes (PVC/ABS), you use solvent cement (glue) for permanent joints where sections of pipe meet directly. However, the joints that allow you to take the trap apart for cleaning (the P-trap connections) must use compression fittings with slip nuts and washers. You need to be able to access the trap to clear clogs.
How tight should the supply lines be when connecting sink water lines?
Supply line connections at the shut-off valves should be snug. Hand-tighten them, then use a wrench to turn them about a quarter to a half turn more. Overtightening can damage the rubber gasket inside the fitting, causing a leak.
How do I know if my sink rough-in measurements are correct?
The simplest way is to measure the height from the cabinet floor up to the center of the existing drain pipe in the wall. This height usually dictates where the outlet of your new P-trap needs to terminate. The ideal height for the trap weir (the top of the curve) is usually 6 inches below the bottom of the sink basin itself.
Is it necessary to use Teflon tape on plastic drain pipe threads?
Teflon tape is used primarily on metal threaded connections (like the water supply lines or faucet shank threads). For plastic drain pipe slip joints, the rubber or nylon washer inside the slip nut provides the seal; Teflon tape is not required and can actually hinder a proper seal on these specific drain fittings.