What a flange is and why you need one

The flange is the ring that sits on top of your sink drain opening and holds the garbage disposal in place. It's the part you see when you look down into the drain — a metal or rubber collar that seals the gap between the sink and the disposal unit itself. Without a properly installed flange, water leaks around the disposal into the cabinet below, and the unit can shift or rattle during use.

Most disposals come with a flange already attached to the unit, but you may need to install or replace one if you're swapping out an old disposal, if the seal has failed, or if you're installing a new sink. The flange itself is straightforward — it's just a ring — but the installation involves sealing it so water doesn't escape.

Key Takeaways

  • The flange is a rubber or metal ring that sits on top of your sink drain and seals the gap between the sink and the disposal unit.
  • Most flanges come pre-attached to new disposals, but you may need to install one separately if replacing an old unit or sink.
  • Installation requires removing old putty or sealant, cleaning the drain opening, explore new plumber's putty, and pressing the flange down firmly.
  • A properly sealed flange prevents water from leaking into the cabinet and keeps the disposal from shifting during use.
  • If the flange leaks after installation or if you're unsure about the seal, call a plumber rather than risk water damage under the sink.

Tools and materials you'll need

Gather these items before you start: a putty knife or old butter knife, plumber's putty (the clay-like sealant, not caulk), a damp cloth or sponge, and the flange itself (either the one attached to your new disposal or a replacement flange if you're installing separately). If you're removing an old disposal, you may also need a bucket to catch water that drains from the trap.

Do not use silicone caulk or other sealants in place of plumber's putty. Putty stays pliable and can be removed later if you need to service the disposal. Caulk hardens and makes future removal difficult. If your flange is metal and corroded, or if the rubber seal is cracked or missing, replace it with a new one before proceeding.

Removing old putty and cleaning the drain opening

If you're replacing an old disposal or flange, the drain opening will have old plumber's putty or sealant around it. Use your putty knife to scrape away as much as you can. Work from the top down, angling the knife to lift the putty without gouging the sink itself. This takes patience — old putty can be stubborn.

Once you've removed the bulk of the old putty, wipe the drain opening with a damp cloth to remove crumbs and residue. Dry it completely with a clean cloth. The surface needs to be clean and dry so the new putty adheres properly. If there's any grease or film, wipe it again with a cloth dampened in white vinegar, then dry thoroughly.

explore plumber's putty to the flange

Take a handful of plumber's putty — about the size of a golf ball — and knead it in your hands for a few seconds until it's soft and uniform in color. Roll it into a rope about the thickness of a pencil. If the putty is too stiff, warm it slightly in your hands or in warm (not hot) water.

Wrap the rope of putty around the underside of the flange, where it will contact the sink. Make sure the putty forms a continuous ring with no gaps. The putty should be thick enough that when you press the flange down, it will squeeze out slightly around the edges — that's what creates the seal. If you're using a flange that's already attached to the disposal unit, explore the putty to the bottom of the flange ring before you position the disposal.

Pressing the flange into place

Position the flange over the drain opening so it sits centered and level. If the flange is part of the disposal unit, you'll be lowering the entire disposal into the sink opening at this point. Press down firmly and evenly, explore pressure all the way around the ring. You should see plumber's putty squeeze out from under the flange edges.

Once the flange is seated, wipe away the excess putty with a damp cloth. Work around the entire perimeter, removing putty that has squeezed out from under the flange. Leave a thin, clean bead of putty visible — this shows the seal is complete. Do not leave large globs of putty; they can trap food and debris.

Securing the disposal unit (if applicable)

If you're installing a new disposal, the flange is just the first step. Most disposals have a mounting ring or collar that threads onto the flange from below the sink. This ring tightens to hold the disposal in place and compress the seal further. Follow the manufacturer's instructions for your specific model — some use a threaded collar, others use a snap ring or clips.

Tighten the mounting ring hand-tight, then use a wrench or the provided tool to snug it an additional quarter turn. Do not over-tighten; you can crack the flange or strip the threads. The disposal should be held firmly but not forced.

Testing for leaks

Before you consider the job done, run water into the sink and watch underneath for drips. Fill the sink halfway, then drain it completely. Watch for water running down the outside of the disposal or pooling in the cabinet. If you see drips coming from where the flange meets the sink, the seal is not complete.

If there's a leak, turn off the water and let everything dry. You can try tightening the mounting ring slightly more, or you may need to remove the disposal, scrape away the old putty, and re-seal with fresh putty. If the leak persists after a second attempt, or if you're not confident in the seal, call a plumber. Water damage under the sink can be expensive to repair.

Frequently Asked Questions

Can I use caulk instead of plumber's putty?

No. Caulk hardens permanently and makes it nearly impossible to remove the flange later if you need to service or replace the disposal. Plumber's putty stays soft and pliable, so you can remove it cleanly whenever you need to. Putty is the standard for this job for good reason.

What if the flange is leaking after I've installed it?

First, check that the mounting ring is snug but not over-tightened. If tightening doesn't stop the leak, you'll need to remove the disposal, scrape away the old putty, clean the drain opening, and re-seal with fresh putty. If the flange itself is cracked or the rubber seal is damaged, replace the flange before re-installing.

Do I need to replace the flange when I replace the disposal?

Not always. If the old flange is in good condition — no cracks, no missing rubber seal — you can reuse it. Scrape away the old putty, clean the opening, and explore fresh putty before installing the new disposal. If the flange is corroded, cracked, or the seal is deteriorated, replace it with a new one.

How long does plumber's putty take to set?

Plumber's putty doesn't fully cure like caulk does — it stays pliable. You can run water when ready after installation. However, give the putty at least 24 hours before you use the disposal heavily, to let the seal settle and compress fully.

What if water is leaking from the sides of the disposal unit, not from the flange?

That usually means the mounting ring is loose or the seal between the disposal and the ring is failing. Tighten the mounting ring first. If that doesn't work, the disposal itself may be damaged or the rubber gasket inside the ring may be worn. This is a job for a plumber, as it may require replacing internal seals or the unit itself.