Your kitchen sink works harder than almost anything else in your home. Think about it — you use it to wash vegetables, rinse dishes, fill pots, scrub your hands dozens of times a day, and even bathe the occasional muddy pet. It’s there every morning and every night, quietly doing its job.
But here’s the thing most people never think about: underneath that familiar basin is a surprisingly detailed system of parts, each one playing a specific role in making sure water flows in cleanly and drains out without a hitch. From the strainer basket sitting at the bottom of your sink bowl to the P-Trap curved beneath your cabinet, every piece matters.
And when one of those pieces fails — a worn-out gasket, a loose slip nut, a cracked tailpiece — you feel it fast. A drip under the cabinet. A foul smell creeping up the drain. A puddle on the floor you can’t explain. Knowing what each part does gives you the power to fix small problems before they become expensive ones, and that’s exactly what this guide is here to help you do.
Kitchen Sink Parts Diagram & Details
The diagram above provides an exploded view of a standard kitchen sink assembly, breaking it down from the basin at the top all the way to the waste line at the bottom. On the right side, you can see the drain assembly components stacked in order — starting with the strainer basket and strainer at the top, moving down through the rubber gasket, flat washer, housing, locknut, and into the lower drain components like the drain elbow, coupling, and waste line. On the left side, the water supply system is shown, including the faucet supply tube, acorn-head supply tubes, sprayer hose, and supply lines that bring hot and cold water up to the faucet.
In the center-bottom area of the diagram, you’ll notice the tailpiece — a vertical brass-colored pipe — connecting the drain assembly above to the swivel P-Trap below, which then feeds into the schedule 40 PVC pipe leading to the waste line. The trap adapter, washers, and glued joints are also clearly labeled, showing how each connection is sealed to prevent leaks. It’s a complete picture of how water enters your sink and how it leaves.
Every part in this diagram has a purpose, and understanding each one helps you troubleshoot problems, make repairs, and even handle a full sink installation with confidence. Let’s walk through them one by one.
1. Strainer Basket
The strainer basket is the part you see and touch most often. It sits right inside the drain opening at the bottom of your sink bowl, and its primary job is to catch food scraps, debris, and other solid bits before they wash down into your plumbing.
Most strainer baskets are made of stainless steel and feature a pattern of small holes or perforations that let water pass through while trapping everything else. You lift it out, dump the collected gunk into the trash, and pop it back in. Simple as that. Some models also have a rubber stopper built in, letting you plug the drain and fill the basin with water for soaking dishes.
Without this little basket, food particles would slide straight into your drain pipes and eventually cause clogs deep in the system — the kind that require a plumber and a hefty bill to clear out.
2. Strainer
Sitting directly beneath the strainer basket is the strainer itself, sometimes called the strainer body or strainer flange. This is the fixed piece that’s mounted into the sink’s drain hole, and it forms the visible ring you see around the opening from above.
The strainer creates a sealed connection between the sink basin and the drain assembly below. Its top flange sits flush against the sink surface, typically bedded in plumber’s putty or a silicone sealant to form a watertight seal. From below, a series of washers and a locknut tighten against it to hold everything in place.
If you’ve ever noticed water slowly seeping around the base of your drain opening, the strainer’s seal is often the culprit. Re-applying putty or replacing the gasket beneath it usually solves the problem in minutes.
3. Rubber Gasket
Right below the strainer, pressed against the underside of the sink, sits the rubber gasket. This thick, flexible ring creates a watertight seal between the strainer body and the bottom of the sink basin.
The gasket compresses when the locknut is tightened from below, forming a snug barrier that prevents water from leaking through the gap between the strainer and the sink surface. Over time, rubber gaskets can dry out, crack, or lose their flexibility, especially in kitchens where hot water is constantly running through the system. When that happens, you’ll start to notice dampness or dripping under your sink — a telltale sign it’s time for a replacement.
4. Flat Washer
The flat washer is a thin, disk-shaped component that sits just below the rubber gasket. Its role is to distribute pressure evenly as the locknut is tightened, helping the gasket compress uniformly around the entire circumference of the drain opening.
Without this washer, the tightening force from the locknut would concentrate unevenly, potentially warping the gasket or leaving gaps where water could seep through. It’s a small, inexpensive piece — but it’s the kind of part that makes the difference between a dry cabinet and a slow, frustrating leak that ruins everything stored beneath your sink.
5. Housing
The housing — sometimes referred to as the strainer housing or drain body — is the cylindrical component that extends downward from the strainer. Think of it as the main structural shell of the drain assembly. It holds the gasket, washer, and other sealing components in position.
This part connects the visible drain opening above to the tailpiece and the rest of the plumbing below. It typically has threading on the outside where the locknut screws on, and a smooth interior channel that guides water straight down into the drainage path.
Because the housing forms the backbone of the upper drain assembly, any cracks or corrosion here can lead to persistent leaks that no amount of tightening will fix. If you spot damage on this piece, replacing the entire strainer assembly is usually the best move.
6. Locknut
The locknut is what holds the entire strainer assembly tight against the sink from underneath. It threads onto the housing and, as you tighten it, compresses the rubber gasket and flat washer firmly against the underside of the basin.
Getting the right amount of torque on this nut is important. Too loose and water seeps through. Too tight and you risk cracking the sink — especially if your sink is made of porcelain or a composite material. A pair of channel-lock pliers or a dedicated strainer wrench makes the job much easier than trying to muscle it by hand.
7. Washer
Positioned below the locknut, the washer provides an additional layer of sealing and cushioning within the drain assembly. It works alongside the rubber gasket above to ensure the connection stays leak-free even as the sink vibrates from daily use — running the garbage disposal, dropping heavy pots in the basin, or scrubbing pans vigorously.
This washer is typically made from rubber or a fiber material and is inexpensive to replace. If you’ve tightened everything and still see a drip, swapping this washer out is one of the first things to try before moving on to more involved repairs.
8. Slip Nut
Slip nuts appear at several points in the kitchen sink drain assembly, and they serve the same basic function each time: they create a removable, watertight connection between two pipes or fittings. You’ll find them where the tailpiece connects to the drain assembly, where pipes meet the P-Trap, and at other key junctions.
Each slip nut works by compressing a washer against the pipe joint as you hand-tighten (and then snug up with pliers). The beauty of slip nut connections is that they’re designed to be taken apart. When you need to clean out a clog, replace a section of pipe, or install a new garbage disposal, slip nuts let you disassemble the plumbing without cutting anything.
One common mistake is over-tightening them, which can crack the nut — particularly the plastic ones. Firm hand pressure plus a quarter-turn with pliers is usually all you need.
9. Dishwasher Waste Nib
The dishwasher waste nib is a small inlet on the side of the drain assembly, and it’s there specifically to accept the drain hose from your dishwasher. When your dishwasher finishes a cycle and pumps out the dirty water, it travels through a hose that connects to this nib, allowing the water to drain through the same plumbing as your sink.
If your kitchen doesn’t have a dishwasher, this nib is typically capped off with a factory-installed plug. One very common installation mistake with new garbage disposals is forgetting to knock out this plug before connecting the dishwasher hose — resulting in a dishwasher that won’t drain at all. A quick tap with a screwdriver and hammer from the inside of the housing pops it right out.
10. Drain Elbow
The drain elbow is an angled pipe fitting — usually a 90-degree bend — that redirects the flow of water from the vertical drain path to a horizontal one. In the diagram, it sits below the main drain assembly and connects to the coupling and waste line leading out to your home’s main drainage system.
This elbow is essential for routing the plumbing within the tight confines of your under-sink cabinet. Without it, you’d need a perfectly vertical path from the drain straight down into the floor, which isn’t practical in most kitchens.
Drain elbows are commonly made of PVC or ABS plastic, and their smooth interior helps waste water flow without catching debris. They connect to adjacent pipes using slip nuts and washers, or in some cases, solvent-welded (glued) joints for a permanent seal.
11. Coupling
The coupling is a straight connector that joins two lengths of pipe together in a continuous line. In the kitchen sink assembly, it bridges the drain elbow to the waste line, creating a smooth, uninterrupted path for water to flow out of your home.
Couplings can be slip-joint style (removable) or glued, depending on where they are in the system. The diagram highlights glued joints at this section, meaning the coupling and adjacent pipes are permanently bonded with PVC cement for a connection that won’t loosen or leak over time.
12. Waste Line
The waste line is the horizontal pipe that carries all the used water from your sink assembly out to the main drain or sewer line in your home. It’s the final stretch of the journey for every drop of water that goes down your kitchen drain.
Typically made from schedule 40 PVC, the waste line runs horizontally (with a slight downward slope for gravity-assisted drainage) through the wall or floor and connects to the broader household plumbing. Making sure this pipe has the correct slope — usually about 1/4 inch of drop per foot of run — is critical. Too flat and water pools inside the pipe, carrying sediment that builds up into a clog over time. Too steep and the water outruns the solids, leaving them stranded in the pipe.
13. Schedule 40 PVC Pipe
Schedule 40 PVC pipe is the standard piping material used in residential drain systems, and you’ll see it in multiple places in this diagram — from the vertical run beneath the P-Trap to the horizontal waste line heading out to the main drain.
“Schedule 40” refers to the wall thickness of the pipe, and it strikes a reliable balance between durability and affordability. It’s strong enough to handle the pressures and temperatures of a kitchen drain system, resistant to corrosion, and lightweight enough to work with easily. The standard size for a kitchen sink drain is 1-1/2 inches in diameter, though some configurations use 2-inch pipe.
PVC is joined using solvent cement (a chemical weld), creating permanent bonds that are extremely strong and leak-resistant. Compared to older cast iron or galvanized steel drain pipes, PVC is a massive upgrade in terms of longevity and ease of maintenance.
14. Swivel P-Trap
The swivel P-Trap is that distinctive U-shaped curve you see under virtually every sink. It’s one of the most important parts of your entire drain system, even though it looks deceptively simple.
Here’s how it works: after water flows down the tailpiece, it fills the curved bottom of the P-Trap before continuing on to the waste line. A small amount of water always remains sitting in the bottom of that curve, and that standing water acts as a seal. It blocks sewer gases — which smell terrible and can actually be hazardous — from rising back up through your pipes and into your kitchen.
The “swivel” designation means this particular P-Trap can rotate and adjust at its connections, making it much easier to align with the tailpiece above and the waste pipe below. This flexibility is especially handy during installation, since your drain outlet and wall pipe rarely line up perfectly. Most residential P-Traps are 1-1/2 inches in diameter for kitchen sinks.
15. Trap Adapter
The trap adapter is a fitting that connects the P-Trap to the drain pipe coming out of the wall (or floor). It provides a transition point between the slip-joint connections of the trap assembly and the permanent glued connections of the waste piping.
On one end, the trap adapter accepts the P-Trap’s slip nut and washer for a removable connection. On the other end, it glues directly into the schedule 40 PVC pipe. This design means you can still disassemble the trap for cleaning without disturbing any of the permanent plumbing cemented into the wall.
16. Supply Lines
Supply lines are the flexible tubes that carry hot and cold water from your home’s shut-off valves up to the faucet. They’re the lifeline of the water delivery side of your sink. In the diagram, you can see them running vertically from the bottom of the cabinet up to the faucet connections.
Modern supply lines are typically braided stainless steel, which gives them both flexibility and durability. Older homes might still have rigid chrome or copper supply tubes, but braided lines have become the go-to choice because they’re easier to install, resist kinking, and are less prone to bursting.
Each supply line has a fitting on each end — one that threads onto the shut-off valve below and one that attaches to the faucet above. It’s a good practice to replace these lines every 8 to 10 years, even if they look fine, since a burst supply line under pressure can flood your kitchen in minutes.
17. Tailpiece
The tailpiece is the straight, vertical pipe that drops down from the bottom of the sink’s drain housing and connects to the P-Trap below. It’s the first section of pipe that water enters after leaving the strainer and drain assembly.
Usually made of brass (like the gold-colored pipe shown in the diagram) or PVC, the tailpiece is typically 1-1/2 inches in diameter and connects at both ends via slip-joint fittings. Its length can be trimmed with a hacksaw if it’s too long for your particular cabinet setup. Brass tailpieces tend to last longer and resist corrosion better than plastic ones, which is why many plumbers prefer them for kitchen sinks.
18. Sprayer Hose
The sprayer hose is the flexible line that connects your sink’s pull-out or side-mounted sprayer to the water supply beneath the faucet. When you press the sprayer trigger or pull out a faucet head, water diverts through this hose to give you a directed, higher-pressure stream for rinsing dishes, cleaning the basin, or washing produce.
Over years of use, the sprayer hose can develop kinks, cracks, or weak spots — especially where it bends repeatedly as you extend and retract the sprayer. A leaking sprayer hose often goes unnoticed for a while because the drip happens inside the cabinet, hidden behind cleaning supplies and trash bags. Checking it occasionally takes only a few seconds and can save you from water damage.
19. Acorn-Head Supply Tubes
Acorn-head supply tubes get their name from the rounded, acorn-shaped compression fittings at their ends. These tubes connect the hot and cold water shut-off valves to the underside of the faucet body, channeling pressurized water up to your tap.
The acorn-shaped head creates a tight seal against the faucet’s inlet ports when tightened with a wrench. Because these connections are under constant water pressure, even a slightly loose fitting can cause a steady drip. The fix is straightforward — snug the connection with a basin wrench (that long-handled tool designed specifically for reaching tight spots under sinks).
These tubes are usually made of braided stainless steel or chrome-plated copper, both of which handle years of daily use without corroding or degrading.
20. Faucet Supply Tube
The faucet supply tube is a dedicated flexible or semi-rigid line that delivers water directly to your faucet. While similar in function to the supply lines and acorn-head tubes, this specific tube is often pre-attached to the faucet body and hangs down ready for connection during installation.
Connecting it is one of the final steps when installing a new faucet. You thread it onto the shut-off valve, hand-tighten the nut, then give it a snug quarter-turn with pliers. Turning the water back on and checking for drips at the connection point takes care of the rest. It’s one of those satisfying moments in a DIY project where you know immediately whether you did it right.
21. Glued Joints
Glued joints — marked in red in the diagram — indicate where PVC pipes and fittings are permanently bonded together using PVC solvent cement. Unlike slip-joint connections that can be taken apart by hand, glued joints are chemical welds that fuse the plastic surfaces into a single, solid piece.
You’ll find these glued connections on the waste-side piping, particularly where the drain elbow meets the coupling and where the waste line connects to the schedule 40 PVC pipe heading into the wall. The solvent cement works by softening the surface of both the pipe and the fitting, and as the solvent evaporates, the two surfaces harden together permanently.
Proper technique matters here. The pipe and fitting should be dry, clean, and primed (with purple PVC primer) before cement is applied. You get about 10 to 15 seconds of working time once the pieces are pushed together, so dry-fitting everything first and marking alignment lines with a pencil is a step you don’t want to skip.
