Introduction
Installing or replacing the plumbing for a kitchen sink is a common home improvement project that can seem daunting to DIYers. However, with proper planning and by following plumbing codes, even beginners can install a fully functional and leak-free kitchen sink drain and supply lines.
In this comprehensive guide, we will walk through the entire process of installing kitchen sink plumbing from start to finish. We will cover how to plan the layout, gather the right tools and materials, install new drain pipes and p-traps, hook up the hot and cold water supply lines, make watertight connections, and test for leaks.
By the end of this guide, you will have gained the knowledge and confidence to tackle this project yourself and enjoy the satisfaction and cost savings of DIY home plumbing. So let’s get started!
Overview of the Kitchen Sink Plumbing Installation Process
Here is a quick overview of the major steps involved in installing or replacing the plumbing for a new kitchen sink:
- Step 1: Turn off the main water supply and disconnect existing sink. Remove old sink and prep the area.
- Step 2: Plan the new drain and water supply layout. Measure for pipe sizes.
- Step 3: Gather the necessary tools and materials. Make sure you have all the right plumbing parts.
- Step 4: Install the new drain outlet and p-trap under the sink. Connect to existing drain line.
- Step 5: Run hot and cold water supply lines from the shutoff valves to the sink faucet.
- Step 6: Make watertight connections at all joints. Attach supply lines to faucet.
- Step 7: Reconnect main water supply and check for leaks. Test sink operation.
Now let’s look at each of these steps in more detail.
Step 1: Turn Off Water Supply and Remove the Old Sink
Before you start removing any pipes or disconnecting anything, it’s crucial to shut off the main water supply to the kitchen. This is typically done via a shutoff valve on the main water line coming into the house, or a separate shutoff just for the kitchen area. Locate this valve and turn it clockwise all the way to the closed position.
Next, you need to disconnect and drain the existing kitchen sink. If you currently have a functional sink, turn on the faucet to allow the lines to drain fully. Check under the sink and find the water supply lines. They are usually copper, braided stainless steel, or flexible plastic tubing. Turn the shutoff valves clockwise to close them off. Disconnect the supply tubes from the faucet using a wrench or pliers.
Once the water is off and drained, you can remove the old sink. Take out any remaining water in the p-trap with a bucket. Disconnect the drain pipes and p-trap assembly from the sink drain tailpiece and from the wall drain. You can keep them intact if they are still functional. Unfasten the sink from the countertop if needed.
With the sink cleared out, you now have space to work. Inspect the existing plumbing coming out of the wall for any signs of leaks, corrosion, or needed repairs. Replace worn out shutoff valves or drain pipes as necessary. Also check the condition of the countertop and make any repairs before installing the new sink.
Step 2: Plan the New Sink Plumbing Layout
Now that the old sink is prepped, you can start planning the layout for the new drain and water supply lines. Here are some important factors to consider:
- Drain pipe size – The drain pipe size must match the discharge size specified by the new sink. Kitchen sinks typically require 1 1/2″ or 1 1/4″ drain pipes.
- Drain position – Most sinks have the drain centered behind the basin. Make sure the drain outlet location will align properly.
- P-trap configuration – Design a p-trap with the proper drain connections and curve to fit under the cabinet. Maintain a water trap depth of 2 inches minimum.
- Supply line position – The hot and cold supply lines should route up to the point where you want the new faucet installed. Leave enough slack for making connections.
- Supply line length – Avoid extremely long supply lines from the shutoff valves to the faucet. Keep them as short as reasonably possible.
- Shutoff valves – Make sure the existing shutoffs are in good shape. Replace them if old, corroded, or damaged. Use quarter-turn ball valves for easy on/off.
Spend time laying out positions for all new plumbing before installation. Reference the sink and faucet manufacturer instructions as needed. This planning will ensure proper fit and function.
Step 3: Gather the Right Plumbing Tools and Materials
Plumbing projects require having the right tools and materials on hand. Here are the essential items you’ll need to install kitchen sink plumbing:
Tools
- Adjustable wrenches
- Pipe wrench
- Basin wrench
- Teflon tape
- Plumber’s putty
- Bucket
- Flashlight
- Safety glasses
Plumbing Materials
- Sink drain outlet and mounting hardware
- Drain p-trap kit with slip nut and washers
- Drain pipe (PVC or metal)
- Sink strainer basket
- Supply lines (braided stainless or flexible polymer)
- Shutoff valves (1/4 turn ball valves recommended)
- Faucet supply line adapters (if needed)
Make sure all plumbing parts match the sizes of your existing water and drain lines. Having spare fittings like couplings and unions is also a good idea. Check that all tools are in proper working order. Turning off the main water supply again before starting work is also a sensible precaution.
Step 4: Install the New Sink Drain Outlet and P-Trap
Once you have all your materials prepped, it’s time to install the new drain plumbing under the sink. Follow these steps:
- Position the sink drain outlet in the sink hole and attach from below with provided hardware. Use plumber’s putty under the rim for a watertight seal.
- Attach the p-trap kit to the drain outlet tailpiece in the cabinet under the sink. Hand tighten the slip nuts over the washers at this point.
- Dry fit the drain pipes from the p-trap to the wall, cutting them to length as needed. Use elbow joints to adjust the angle and direction.
- Connect the assembled p-trap to the drain pipes leading to the wall with washers and slip nuts. Tighten all joints securely with wrenches.
- Attach the drain pipe coming out of the wall to the p-trap assembly. The p-trap must slope 1/4 inch per foot downward towards the wall.
- Confirm proper drainage by pouring water into the sink drain. Tighten any joints that leak.
Be very careful when tightening the slip nuts on the p-trap assembly. Over-tightening can easily crack the plastic components. The p-trap must maintain a water seal, so test for leaks before moving on.
Step 5: Install Shutoff Valves and Water Supply Lines
With the new drain operational, you can work on the water supply plumbing:
- Replace any old shutoff valves under the sink with new 1/4-turn ball valves. Use pipe joint compound on the threads.
- Measure and cut hot and cold supply lines to reach from the shutoffs to the faucet inlet ports. Leave some extra length.
- Secure the lines with attachment nuts and washers at the shutoff valve and faucet connections. Use two wrenches to tighten.
- Bend and orient the supply tubes as needed for a clean installation. Avoid kinks by making wide curves.
- Connect the ends of the supply tubes to the faucet inlet ports. Most use 3/8″ compression nuts. Make sure washers are seated properly.
- Turn on shutoff valves briefly to flush debris from supply lines. Shut them and reconnect faucet.
Take care not to cross-thread fittings and be sure to use wrenches for secure connections. With everything attached, you’re almost ready to test for leaks.
Step 6: Make Watertight Connections and Attach Faucet
Before turning the water back on, it’s important to seal up any potential leaks:
- Wrap all threaded fittings with Teflon tape to prevent leaks. Go around threads a few times clockwise.
- Add a small amount of plumber’s putty around the drain outlet underneath the sink flange. Smooth with a wet finger for a tight seal.
- Secure the sink and faucet properly to the countertop per the manufacturer instructions. Tighten any mounting nuts and bolts.
- Turn on shutoff valves and inspect for drips. Tighten any leaky joints with wrenches.
- Attach sink sprayer hose to the faucet spray outlet. Make sure the gasket seals properly.
Go under the sink and use a flashlight to double check all fittings and connections. Look for signs of water dripping or wet spots and immediately tighten anytime you find a leak. Taking your time here prevents major leaks down the road.
Step 7: Reconnect Main Water Supply and Test Sink
After confirming no leaks underneath, complete the job by:
- Turning back on the main water supply. Turn the main shutoff valve counterclockwise to fully open.
- Removing the drain outlet plug and turning on the sink faucet. Let water run to clear any debris.
- Checking for leaks above and below the sink. Tighten any dripping connections.
- Testing sink operation by plugging the basin and filling it with water. Check the drain.
- Run water into the sink strainer and confirm proper draining with no leaks or backups.
- Check for secure connections on the p-trap assembly and supply line fittings.
Finally, turn on the faucet and enjoy your newly installed kitchen sink! Be sure to monitor during the first few days of use and tighten anything that may become loose.
FAQs About Installing Kitchen Sink Plumbing
Here are answers to some frequently asked questions about installing kitchen sink plumbing:
What pipe material should be used for the drain line?
The drain and p-trap assembly can be PVC, black ABS plastic, or chromed metal pipe. PVC is the most common. Make sure slip-joint connections fit properly.
How do I remove old corroded supply line fittings?
Penetrating oil can help loosen corroded threads. Beware that old compression fittings may spin; cut off the tubing if needed. Replace with new supply tubes.
What is the proper p-trap configuration?
The p-trap must have a vertical leg into the drain, a horizontal run sloping 1/4″ per foot, and a vertical leg with a minimum 2″ depth to maintain the water trap seal.
Should I use Teflon tape on compression fittings?
No, Teflon tape is not needed on slip-joint compression connections with washers. Only use tape on threaded pipe connections.
Can I position my sink drain on the left or right?
Yes, you can install the drain assembly on either side under the sink basin. Make sure to align it properly when tightening the mounting gasket.
How do I narrow down the source of a leak?
Turn on the water supply and watch directly to see where drips first appear. Or fill the basin and wait to see if water appears under the sink. Check each joint.
What do I do if the new faucet doesn’t fit my existing supply lines?
Use adapter fittings to convert supply line sizes as needed. For example, convert 3/8″ compression tubing to 1/2″ male pipe threads.
Why does my drain gurgle after installing the new sink?
A gurgling sound usually means there is an airflow issue with the p-trap assembly. Make sure all slip nuts are tight and the trap is filled with water.
Conclusion
Installing the plumbing for a new kitchen sink does not have to be an intimidating DIY project. By following the steps outlined in this guide, you can successfully replace your sink drain lines, p-trap, supply tubes, faucet, and shutoff valves.
The keys are proper planning, using quality plumbing materials, making watertight joints, and testing for leaks before completion. Expect the job to take 4-6 hours your first time. Working slowly and methodically is the best approach.
Acquiring plumbing skills allows you to save on labor costs and take care of home repairs yourself. And completing a professional-looking sink installation can provide great personal satisfaction. We hope these plumbing tips give you the knowledge and confidence to tackle your next sink hookup project.