Flanged Tailpieces

Despite sharing a name with heavy industrial pipe flanges, this part is almost always one thing under a residential or light-commercial sink: a flanged drain tailpiece. It’s the straight vertical pipe that drops from the strainer body to the P-trap inlet, forming the first segment of the sink drain assembly. The job before buying one is simple but unforgiving. Match the diameter, the length, and the material to the sink and trap you actually have. Get the diameter wrong and nothing seats. Get the length wrong and the slip joint won’t reach.

For broader project planning, explore WBC’s building materials resources.

The single most important fact: bathroom sink installations are normally completed with 1-1/4” tubular products, but 1-1/2” will also work, while kitchen sink installations can only be completed with 1-1/2” tubular products. Buy to that rule and most of the guesswork disappears.

What It Is and How It Fits

A tailpiece carries wastewater downhill. Nothing more complicated than that. Tailpieces are made from thin-wall tubing — thinner than DWV pipe — because they carry wastewater by gravity rather than under pressure.

The connections are what matter on a straight tailpiece. It connects at the top via a slip nut and rubber or nylon washer that threads onto the strainer body tailpiece shank, and at the bottom via another slip-joint connection to the P-trap arm.

A flanged version changes the top end. Flanged tailpieces have a built-in flange at the top that sits under the strainer body and seals with a gasket, eliminating the need for a separate slip-nut connection. That built-in seal is the whole point — fewer parts to leak at the strainer, and a cleaner connection up top.

Sizes, Lengths, and Materials

Diameter comes first, then length, then material. The diameter is dictated by what’s at the wall: the trap adapter connection to the branch drain in the wall determines the largest size of tubular product that can be connected with a slip nut and washer, and that connection can also be reduced for 1-1/4” tubular assemblies with a reducing washer and slip nut.

For length, most jobs are short. The standard length is 6 to 8 inches, but 12-inch extensions are available when the trap is positioned lower than usual due to cabinet depth or non-standard rough-in height. Spec sheets run longer than that — flanged strainer tailpieces come in lengths up to 18 and 20 inches for deep or offset setups.

Material is the third call. Tailpieces are commonly chrome-plated brass, ABS plastic, or PVC — chrome brass is the traditional choice for exposed installations where the under-sink plumbing is visible, such as pedestal sinks and wall-mounted vanities, while plastic is widely used in concealed or budget applications. On brass, thickness is graded. Brass tubular products are offered in three different thicknesses: 17 gauge is the thickest, often referred to as commercial grade; 20 gauge is mid-range; 22 gauge is the thinnest, sometimes called “budget grade.”

Spec	Detail
Bathroom sink diameter	1-1/4” (1-1/2” also works)
Kitchen sink diameter	1-1/2” required
Standard length	6–8 inches
Extension lengths	12, 16, 18, 20 inches
Plastic materials	PVC, ABS, polypropylene
Brass gauges	17 GA (commercial), 20 GA (mid), 22 GA (budget)

The sizes Western Building Center carries in this category track those standards — flanged sink tailpieces in 1-1/2” with flange in 22-gauge, slip-joint extension tubes in both 1-1/4” and 1-1/2” diameters from 6 up to 16 inches, chrome tubular flanges, and the slip-joint nuts and washers in 1-1/4” and 1-1/2” sizes that finish the connections.

A note on the chemical-resistant variant: some specialty tailpieces are made from polypropylene for resistance to chemicals used in laboratory or darkroom sinks.

Variants for Dishwashers, Disposers, and Double Bowls

A plain tube doesn’t cover every setup. Match the variant to what’s hanging off the sink.

Straight is the default. Straight tailpieces are the most common form and consist of a plain tube with no branching connections.

Got a dishwasher and no disposal? You need the side inlet. Some tailpieces include a side inlet port — often called a tee tailpiece or dishwasher tailpiece — with a barbed branch connection sized for the dishwasher drain hose, typically 7/8 inch outside diameter, used when no garbage disposal is present to receive the dishwasher discharge line. The branch port includes a removable plastic knockout that must be popped out before connecting the hose. Western Building Center stocks dishwasher tailpieces in 1-1/2” x 8” and slip-joint versions.

For disposer installs that need two tailpieces, a cut-to-length double-end is the workhorse. A 1-1/2” slip joint inlet on both ends, in 6-, 8-, 12-, and 16-inch lengths, ideal for disposal applications where two tailpieces are needed and able to be cut to length, meeting ASTM F 409 and IAPMO listed.

When you want to dial in length without sawing, telescoping is the answer. Adjustable tailpieces telescope to allow fine-tuning of the vertical length without cutting.

And the size-bridging part worth knowing: a reducing flanged tailpiece is used when connecting a 1-1/2” IPS drain to a 1-1/4” trap, with a fully polished and plated brass nut that threads onto the drain and includes a washer.

Double-bowl kitchen sinks build off these pieces. In double-bowl kitchen sinks, each bowl has its own tailpiece that connects to a tee fitting or continuous waste assembly before reaching the single P-trap, and bar sinks and prep sinks in islands also use tailpieces, often requiring longer runs to reach offset traps behind or beside the cabinet.

Choosing and Installing It Right

Buy by matching, not by eyeballing. For plumbing work, that usually means matching the part to the system it serves, the code requirements that apply locally, and the manufacturer’s installation instructions — a substitution that appears to fit can still create problems if its pipe size, finish, or listing does not match the job.

When you replace one, the install steps are short. Position the flanged end under the strainer and secure it into place, ensuring that the rubber or foam gasket is properly seated to create a watertight seal. Then connect to the trap and tighten with an adjustable wrench — but be cautious not to over-tighten, as this can damage the fittings. Slip nuts seat by hand. They’re not supposed to be cranked down with a pipe wrench.

Plan on replacing these. They are one of the most frequently replaced plumbing components because of their position in a wet, corrosion-prone environment directly below the drain opening where detergents, food acids, and standing water accelerate deterioration. That’s an argument for keeping the connection accessible. Accessibility matters because parts that need adjustment, inspection, cleaning, or replacement should not be permanently trapped behind finishes.

Montana adds two wrinkles. First, location drives wear. A tailpiece in a damp cabinet, unconditioned attic, exterior wall, or high-use area may age faster than one in a clean, dry, stable location. That covers a lot of cabins, seasonal places, and rentals where the under-sink cabinet sits cold all winter. Second, water chemistry. Local climate matters as well — sun exposure, freeze-thaw cycles, hard water, and repeated use can all change how the part ages. Hard water leaves mineral scale on plastic and washers. Check the slip joints periodically. A corroded tailpiece may show green patina on brass or white mineral deposits on plastic.

When access is tight and reopening a cabinet later is a pain, spend up. When the component is difficult to access after construction, spending more on a durable version is often cheaper than opening finished surfaces later.

Frequently Asked Questions

What size tailpiece does a kitchen sink need? A kitchen sink needs 1-1/2”. Kitchen sink installations can only be completed with 1-1/2” tubular products. Bathrooms typically use 1-1/4”, though 1-1/2” will also work there.

What’s the difference between a flanged tailpiece and a straight one? The top connection. Flanged tailpieces have a built-in flange at the top that sits under the strainer body and seals with a gasket, eliminating the need for a separate slip-nut connection. A straight tailpiece relies on a separate slip nut and washer at the strainer shank.

How long should a tailpiece be? Most are short. The standard length is 6 to 8 inches, but 12-inch extensions are available when the trap is positioned lower than usual due to cabinet depth or non-standard rough-in height. Cut-to-length and telescoping options handle the odd dimensions.

Brass or plastic? Depends on whether you’ll see it. Chrome brass is the traditional choice for exposed installations where the under-sink plumbing is visible, such as pedestal sinks and wall-mounted vanities, while plastic is widely used in concealed or budget applications. On brass, 17 gauge is the thickest, often called commercial grade.

How do I connect a dishwasher if there’s no garbage disposal? Use a tee/dishwasher tailpiece. The branch, typically 7/8 inch outside diameter, is used when no garbage disposal is present to receive the dishwasher discharge line, and the branch port includes a removable plastic knockout that must be popped out before connecting the hose.

Can I connect a 1-1/2” drain to a 1-1/4” trap? Yes, with the right part. A reducing flanged tailpiece is used when connecting a 1-1/2” IPS drain to a 1-1/4” trap, with a brass nut that threads onto the drain and an included washer. A reducing washer and slip nut can also step a connection down to 1-1/4”.

Why does my tailpiece keep leaking? Often it’s the connection, not the tube. A leaking tailpiece often leaves water stains or a slow drip visible on the outside of the pipe near the slip-nut connections. Reseat the washer and hand-tighten — over-cranking damages fittings. In hard-water areas, mineral buildup on washers is a common culprit, so inspect the slip joints during routine checks.