Fixing the Seal on a Tower- or Canister-Style Flush Valve

A leaky flush valve can be annoying and waste water. Fortunately, fixing the seal on a tower- or canister-style flush valve is usually a straightforward DIY project that doesn’t require any special tools. In this comprehensive guide, we’ll walk through the steps to diagnose and replace the seal on this common type of flush valve found in many toilets.

What is a Tower- or Canister-Style Flush Valve?

A tower- or canister-style flush valve is the tall plastic cylindrical part inside the toilet tank that releases water from the tank into the toilet bowl when you flush. It consists of an outer canister that encloses the flush valve seal and flapper.

When you flush the toilet, the flush valve seal lifts up off the flush valve seat, allowing the water in the tank to empty into the bowl. As the tank empties, the flush valve seal then settles back down onto the flush valve seat, sealing off the water line again so the tank can refill.

Diagram of a tower-style flush valve

These types of flush valves are common in both residential and commercial toilets. They provide a reliable flush with a large 3” or 4” flush valve opening.

Brands like Fluidmaster and Korky are two of the most popular manufacturers of replacement parts for tower/canister flush valves.

Symptoms of a Faulty Flush Valve Seal

How can you tell if the flush valve seal needs to be replaced? Here are some common signs:

  • Toilet continues to run after flushing, causing the tank to empty into the bowl.
  • Water constantly trickles into the toilet bowl, leading to higher than normal water bills.
  • Having to jiggle the flush lever to get the toilet to fully flush and seal.
  • Finding water on the outside of the toilet tank or bowl after flushing.
  • Seeing mineral deposits around the flush valve from leaking water.

If you notice any of these issues, it likely means the rubber seal is worn out or misaligned and no longer sealing the valve opening properly. Replacing the flush valve seal should resolve these running toilet problems.

How to Replace the Flush Valve Seal

Fixing a canister flush valve seal is a relatively easy DIY job. Here are the step-by-step instructions:

Supplies Needed

  • New flush valve seal designed for your model of flush valve
  • Adjustable wrench
  • Rag or towel

Step 1: Turn Off Water Supply

Start by shutting off the water supply line behind the toilet. Flush the toilet to empty the tank. Sponge up any remaining water in the tank or bowl.

Turning off toilet water supply

Tip: Place a rag around the flexible water supply line to prevent scratching the toilet surface when you disconnect it.

Step 2: Remove Old Flush Valve Seal

On the underside of the flush valve, loosen and remove the large nut holding the flush valve seal in place.

Loosening flush valve nut

With the nut removed, detach the old flush valve seal from the valve body. Make note of how the seal is oriented for later.

Clean mineral deposits or gunk off the flush valve seat. Verify the flush valve seat is not cracked.

Step 3: Install New Flush Valve Seal

The new flush valve seal will come with directions specific to that model. But in general, you follow these tips:

  • Make sure the seal direction matches how the old one came off. It is usually a certain way to make the flapper face inward.
  • Grease the seal rim or apply lubricant so it slides on easier over the valve body.
  • Press the seal evenly and completely down over the valve body.
  • Tighten the seal nut carefully and firmly. Do not overtighten.
Installing new flush valve seal

Step 4: Reattach Water Line and Turn On Water

Reconnect the water supply line to the tank fill valve and turn on the water. Let the tank fill and check for any leaks.

Step 5: Test Flush

Perform a test flush. The new flush valve seal should open fully and seal again after flushing. If it still runs, you may need to adjust the chain length or flush valve nut some more.

And that’s it! With a few simple steps and minutes of effort, you can replace the leaky flush valve seal and stop that annoying trickling sound. Take action as soon as you notice symptoms to prevent wasting water.

FAQ About Fixing Canister Flush Valves

Here are answers to some frequently asked questions about servicing tower or canister style flush valves:

What if the new seal doesn’t fit my flush valve?

  • Buy a universal jumbo seal that should flex to fit most valves. You can also bring the old seal to the hardware store to match up replacement sizes.

How do I remove a stuck flush valve nut?

  • Spray lubricant around the nut and let it soak in for 5-10 minutes. Tap gently with a wrench to unstick the nut. Avoid over-torquing it.

Why does my flush valve leak between the tank and bowl?

  • Make sure the sponge gasket around the tank outlet is in good shape. Replace if deteriorated. Verify the lock nut is tight.

What if water keeps running into the overflow tube?

  • Adjust the float cup lower on the fill valve rod or replace the flapper seal if worn out. The fill valve may need to be replaced.

Can I replace my 3” flush valve with a 4” one?

  • Yes, increasing flush valve size can improve flush power. Just make sure your toilet tank is tall enough to accommodate it.

Should I replace a leaky gasket under the flush valve?

  • Absolutely. A worn tank to bowl gasket can lead to leaks and loosen the flush valve. It seals the valve shank to the tank.

How often should the flush valve seal be replaced?

  • Around every 5-7 years for residential use. More frequent in high traffic bathrooms. Just replace as needed when leaks occur.


A faulty flush valve seal is one of the most common repairs for a toilet that runs continuously or loses its prime. Thankfully, the fix is straightforward with a few basic tools and a replacement seal.

The key steps are shutting off the water, removing the old seal, lubricating and attaching the new seal properly, and adjusting as needed to ensure a watertight flush valve. Done right, this repair can restore your toilet’s proper flushing function and stop wasted water.

For other toilet tank troubleshooting tips, feel free to contact us or call our service team. Our trained technicians can diagnose any toilet or plumbing issue. We’re here to help!