Why is my kitchen sink leaking under the basket strainer?

The most common cause is failed plumber's putty around the strainer body flange. Over time, the putty dries out, shrinks, and loses its seal. To fix it, unscrew the locknut from below, lift the strainer body out of the sink, clean off the old putty, apply a fresh rope of plumber's putty under the flange, reseat the body, and retighten the locknut.

What size basket strainer fits my kitchen sink?

The vast majority of kitchen sinks use a standard 3-1/2 inch drain opening, and nearly all replacement basket strainers are designed for this size. Measure the diameter of the drain hole in the sink bowl if you are unsure. Oversized farmhouse or specialty sinks occasionally use different sizes — check the sink manufacturer's specifications.

Do I need plumber's putty when installing a basket strainer?

Yes, unless the replacement strainer specifically states it uses a rubber gasket in place of putty. Traditional basket strainer bodies require plumber's putty applied as a rope under the flange to create a watertight seal at the sink surface. Silicone caulk can be used as an alternative on some surfaces but can make future removal difficult.

How often should I clean the basket strainer?

Empty the basket after every few uses or whenever it becomes full enough to slow drainage. A full basket reduces flow and can cause standing water in the sink. Rinse it under running water and scrub periodically with dish soap to prevent odor and biofilm buildup.

Does replacing a basket strainer require a permit?

No permit is required to replace a basket strainer. It is a like-for-like repair to an existing fixture and is within the scope of homeowner maintenance in all US jurisdictions.

Basket Strainer — Kitchen Sink Drain Fitting Explained

A basket strainer is a drain fitting installed at the bottom of a kitchen sink that holds a removable perforated basket to catch food debris while allowing water to flow through to the drain.

Basket Strainer diagram — labeled parts and installation context

What It Is

A basket strainer is a two-part assembly: a drain body that threads permanently into the sink drain opening, and a removable stainless-steel or plastic basket that sits inside the body. The body is sealed to the sink with plumber's putty on the top flange and a rubber gasket, friction ring, and locknut on the underside. A crossbar at the bottom of the body supports the basket and connects to the drain tailpiece below.

The basket itself has small perforations — typically 1/16 to 1/8 inch in diameter — that let water drain while catching food particles, bottle caps, and small utensils that would otherwise block the drain. Most baskets have a center post that aligns with a stopper mechanism — pressing down or twisting the basket converts the drain into a sealed basin for soaking. Some baskets use a separate rubber stopper instead.

Basket strainers are the first component in the kitchen sink drain stack and connect directly to the drain tailpiece that leads to the p-trap and household drain. The body typically has a 1-1/2 inch tailpiece connection on the underside, which is the standard drain size for residential kitchen sinks.

Types

Standard basket strainers fit the universal 3-1/2 inch sink drain opening found in nearly all kitchen sinks. The body is typically chrome-plated brass or stainless steel, and the basket depth is about 1-1/4 inches.

Pullout strainers allow the basket to be removed by pulling straight up rather than twisting — useful with wet hands. They use a spring-loaded post that releases with upward pressure.

Deep cup strainers have a basket depth of 2 inches or more, holding significantly more debris before needing to be emptied. These are preferred in high-use kitchens and commercial prep sinks.

Disposal flanges are a related fitting used when a garbage disposal is installed — the disposal body threads directly onto the flange rather than a tailpiece. The flange uses the same 3-1/2 inch sink opening and the same putty seal method as a basket strainer.

Where It Is Used

Basket strainers are installed in every kitchen sink drain opening. Double-bowl sinks require two strainers — one per bowl. Utility sinks and laundry tubs typically use a simpler flat strainer or mesh screen rather than a basket-style assembly because those sinks handle less food debris.

In commercial kitchens, basket strainers are often paired with a downstream grease trap and must be emptied more frequently to maintain flow. Restaurant health codes may specify the maximum allowable debris accumulation before the strainer must be cleaned.

How to Identify One

Look down into the kitchen sink drain. The chrome or stainless ring at the drain opening is the strainer body flange, which sits flush with the sink surface. Lift out the perforated cup inside — that is the basket. The basket has a handle, post, or knob at its center for easy removal. If you do not see a removable basket, the sink may have a garbage disposal flange instead.

Underneath the sink, the strainer body extends about two inches below the sink bottom and connects to the tailpiece with a slip-joint nut. A rubber gasket and a metal friction ring sit between the sink and the locknut, providing the watertight seal on the underside.

Replacement

Basket strainers wear out when the plumber's putty seal fails (causing leaks under the sink), when the locknut corrodes, or when the basket itself corrodes or loses its seal. Replacement costs $10–$40 for the part and is a straightforward DIY repair: remove the locknut from below with basket-strainer pliers or a screwdriver in the crossbar slots, pull the old body up through the sink, clean the sink surface of old putty, and install the new one with a fresh rope of plumber's putty rolled to about 1/2-inch diameter. Retighten the locknut until putty squeezes out evenly around the flange, then trim the excess. No permit is required.

If the sink is made of a porous material such as natural stone or marble, the strainer manufacturer may recommend silicone sealant instead of plumber's putty, as putty can stain certain stone surfaces over time.