Check that this guide fits your situation.
Use this guide when
An accessible standard gravity toilet with an internal running-water problem, sound porcelain and a supply stop that closes gently and reliably.
Do not use it for
Pressure-assisted vessels, concealed or powered systems, damaged porcelain, an overflowing bowl, external leaks, seized stops or unfamiliar rigid connections.
Stop and get help if
- The supply stop will not close gently, begins leaking, or water continues entering with it closed.
- You find cracked porcelain, a damaged flush-valve seat or overflow tube, or an external leak.
- The bowl is rising, sewage is present, or water reaches electrical equipment.
- Hardware is inaccessible, corroded or requires force; the exact model or part fit is uncertain.
Watch the illustrated walkthrough.
4:00 captioned animation. No audio; pause to read. The complete guide and your model’s instructions cover details that vary by equipment.
Open the video watch page and transcript →Supplies
- Phone for model numbers and before photos
- Towels, sponge and small bucket
- Food coloring or toilet leak-test tablet
- Soft cloth and optional gloves
- Matched flapper, seal or fill valve with its instructions
- Small adjustable wrench or pliers only where permitted
- Compatible supply connector if the existing one is damaged
A quiet toilet starts with the right diagnosis.
To fix a running toilet, first watch whether the tank overfills or loses water between flushes. Adjust a snagged chain, stuck float or misplaced refill tube before buying parts. Replace a matched flapper or canister seal for an outlet leak; repair or replace the fill valve when the inlet will not shut off. Isolate the water before disassembly and finish with dye and external-leak checks.
Updated October 7, 2026 · For accessible gravity toilets · Exact equipment and product instructions take priorityFirst, catch the culprit
Your toilet is not being dramatic. It is telling you that water is entering when it should stop, or escaping when it should stay put. Watch one refill with the lid off.
Use the clogged-toilet first-response guide →
| What you notice | What to check | What to do |
|---|---|---|
| Water spills into the tall overflow tube | The tank level keeps rising, or the float touches the wall or another part. | Free the float and lower the shutoff setting. If the valve still admits water at its shutoff position, service or replace it.Go to this check → |
| It refills by itself every so often | The tank loses water between flushes; this is often called ghost flushing. | Check the chain, flapper or canister seal, and refill-tube placement. Test for a tank-to-bowl leak.Go to this check → |
| A jiggle of the handle stops it | The handle sticks, the chain snags, or the flapper hangs open. | Let the handle return freely and adjust the chain before replacing parts.Go to this check → |
| Hissing continues below the overflow rim | Look for moving water in the bowl and compare the tank level over time. | A leaking seal can keep a healthy fill valve busy. Isolate tank loss before blaming the noisy part.Go to this check → |
| Water is on the floor or outside the tank | Look from a dry area at the supply connection, tank bottom and porcelain. | Shut off the supply if safe. An external leak needs its own diagnosis; do not continue an internal-leak repair.Go to this check → |
| The bowl rises toward the rim | This is a drainage problem, not simply a running tank. | Stop flushing. Use the clogged-toilet first-response guide or call for help.Go to this check → |
Meet the tiny team inside your tank
In a standard gravity toilet, the fill valve brings water in and the flapper lets it out. They do different jobs.
- Fill valve + float: the inlet assembly senses the rising tank water and shuts off the supply. Older versions may use a ball on an arm instead of a float cup.
- Flapper + chain: the handle lifts a hinged seal so tank water can rush into the bowl. The flapper then closes against the flush-valve seat.
- Overflow tube: the upright opening directs excess tank water into the bowl. Water continuously spilling over its rim is a clue to overfilling.
- Refill tube: the small hose sends some water into the bowl during refill to restore its water level. On an open overflow tube, use the supplied clip; do not push the hose down inside.
- Canister or tower: some toilets lift a cylinder instead of a hinged flapper. They need a compatible seal or repair kit, not a flapper selected by appearance.
- Waterline mark: the toilet maker’s intended tank fill level. This is different from a fill valve’s critical-level mark.
The ten-minute “is it leaking?” test
A few drops of food coloring can reveal an otherwise silent tank-to-bowl leak. Diagnose before you take anything apart.
Start after adding dye. Leave the toilet unflushed until the wait ends.
Ready when you are.Keep this page open. The timer uses elapsed time if your browser pauses updates.For a second check, let the tank refill, gently close a working supply stop and mark the tank water level with a pencil. Wait about 25–30 minutes without flushing. A falling level means water is escaping from the tank; look outside as well as in the bowl. Restore the supply after a supervised test if there is no external leak. Do not leave the tank unobserved if you suspect a floor leak.
- 01
Let the tank finish filling
Lift the lid with both hands and place it flat on a towel, away from the tank edge. Observe whether water is already spilling over the overflow rim. If it is, address overfilling first; dye carried over the rim does not prove a bad flapper.
Why this mattersYou need to distinguish an inlet problem from a leak at the outlet seal. - 02
Add a few drops and wait
Put a few drops of food coloring or a toilet leak-test tablet into the tank, not the bowl. Do not flush for 10 minutes. Keep children and pets away from the open tank.
Why this mattersColor can trace water moving from the tank to the bowl without a flush. - 03
Read the result, then flush away the dye
Color in the bowl shows that tank water is reaching it. With no overfilling, check the flapper or canister seal, chain, refill-tube routing and flush-valve body. Flush promptly after the test to reduce staining. A clear bowl after 10 minutes does not rule out a very slow or intermittent leak.
Why this mattersThe result identifies a leak path, but it does not automatically identify the failed part.
Try these free fixes before the hardware store
Sometimes the winning part costs nothing. Change one thing at a time, then watch a complete refill.
- Release a snagged chain. With the handle at rest, the flapper must lie flat without being pulled upward. Leave a little slack according to the flapper instructions; many specify roughly one or two loose links. A fixed half-inch rule does not fit every design.
- Keep extra chain out of the seal. Secure the loose tail so it cannot slip beneath the flapper. Check that the handle returns without sticking; do not force or over-tighten its mounting hardware.
- Give the float room. Remove a hose or chain that interferes with its travel. Adjust the float using the valve’s screw or clip and instructions; do not bend unfamiliar parts.
- Set the tank to its marked waterline. If there is no mark, find the toilet’s manual. Many gravity tanks stop roughly 1/2–1 inch below the overflow rim, but the specified level for your model takes priority.
- Correct refill-hose routing. Clip it above an open overflow tube so the stream enters the opening without the hose end being submerged. For a dedicated canister port, use the toilet maker’s connection method.
- With the water off and tank drained, wipe the flapper and seating ring with a soft cloth. Grit can break the seal. Do not sand the seat or add grease, petroleum jelly, glue or sealant.
Buy the right part once
“Universal” means broad compatibility, not every toilet. A quick photo session beats a second trip to the store.
Plan roughly 15–30 minutes for an accessible flapper change or 30–60 minutes for a fill valve, plus diagnosis and shopping. These are planning estimates, not promises. Retail prices vary by fit and supplier; check the compatible part’s current price rather than assuming a flat cost. Usually neither job requires removing the tank or toilet.
- Photograph the full tank, old part, refill connection and any model numbers. The tank number may be stamped or printed inside the porcelain or under the lid; do not rely only on a brand name.
- For a flapper, match the flush opening and mounting design, plus the toilet’s flush volume. Common nominal sizes are 2 and 3 inches. The rubber’s outside width is not the opening size; use the model’s parts list or the maker’s fit guide.
- For a canister, tower or dual-flush valve, match the exact seal and model. Ring diameter, profile and mounting mechanism all matter.
- For a fill valve, confirm gravity-tank compatibility, adjustable height, lid clearance, supply connection and any toilet-specific adapter. Low-profile, concealed and specialty tanks may need a dedicated part.
- Choose a seal labeled for the water-treatment conditions it will face, such as chlorine/chloramine resistance. No material lasts forever, and local treatment varies by provider.
- Inspect the supply connector before starting. Replace a corroded, cracked, kinked or damaged connector with the specified compatible type. A rigid line, seized connection or hidden mounting nut is a good reason to call.
- Keep the instructions and package. An adjustable flapper or bowl-refill dial needs the setting appropriate to the toilet; “more water” is not automatically better.
Path A: replace a hinged flapper
Choose this path when the tank loses water through a flapper-style outlet and chain adjustment or gentle cleaning has not solved it.
- 01
Close the supply and empty the tank
Gently close the toilet’s supply stop. Most multi-turn valves close clockwise; quarter-turn valves turn only 90 degrees. Do not force it. Flush and hold the handle to release tank water. Confirm the inlet has stopped before putting hands inside. Sponge residual water if needed.
Why this mattersA drained, isolated tank makes it easier to see the mounting points and seat. - 02
Photograph, unhook and lift out
Take a photo of the chain attachment and flapper hinges. Unclip the chain from the lever, then release the old flapper from its mounting ears or collar using its intended method. Avoid bending or snapping the overflow tube. If the mounting is unfamiliar, look up the exact model before proceeding.
Why this mattersA reference photo helps restore the layout and avoids damaging brittle plastic. - 03
Clean and inspect the seat
Wipe the sealing rim with a soft damp cloth. Remove loose grit without scratching it. Inspect for cracks, chips or a distorted seating surface. Stop if the seat or overflow tube is damaged; a flapper cannot seal a broken flush-valve body.
Why this mattersThe new rubber needs a smooth, sound surface. - 04
Fit the matched flapper
Attach the replacement using the package’s hinge or collar instructions. Some parts support more than one mounting style; configure only the one specified for your toilet. Set any adjustable dial or float according to the model’s flush-volume guidance.
Why this mattersA correctly sized part can still leak or flush poorly when mounted or calibrated incorrectly. - 05
Set chain slack and check travel
Connect the chain near the position shown in your photo. Let the flapper sit flat with slight slack, often one or two links when the part instructions specify that. Secure the excess tail. Operate the handle gently: the flapper should lift freely and return without catching the hose, chain or valve.
Why this mattersTension holds it open; excessive loose chain can snag or get under the seal. - 06
Refill, flush and verify
Open the supply slowly and watch the refill. Flush two or three times, allowing the tank to refill each time. Confirm the flapper reseats and the handle returns. Repeat the dye test without flushing during its wait, then flush out the dye. Finish with the leak checks below.
Why this mattersOne quiet refill is encouraging; repeat operation and a leak test verify the repair more thoroughly.
No flapper? Use the canister-seal path
If a cylinder or tower lifts vertically, its sealing ring plays the flapper’s role. The release mechanism depends on the model.
- 01
Identify the exact assembly
Find the tank model and its manufacturer’s seal-replacement instructions. Match the replacement ring or gasket by model, not just color or diameter. Do not fit a hinged flapper to a tower.
Why this mattersSimilar-looking seals and locking mechanisms are not necessarily interchangeable. - 02
Isolate, drain and release as instructed
Close a working supply stop gently, flush and remove remaining water as needed. Photograph the linkage and refill connection. Follow the model’s release steps; some use a twist lock, others a retaining part. Do not assume every tower turns the same direction or force a stuck guide.
Why this mattersForcing the assembly can break the flush valve and turn a seal job into a larger repair. - 03
Replace the ring and reassemble
Remove the worn ring as directed, wipe the seat with a soft cloth and inspect it for damage. Install the matched seal evenly without stretching or twisting it. Refit and secure the assembly, reconnect the hose or linkage in the specified position, and check free travel.
Why this mattersA pinched ring, unlocked tower or misplaced hose can keep a new seal from working. - 04
Test like a flapper repair
Restore water slowly. Watch several flushes and complete the dye test and external-leak checks. If the seal is correct but water still escapes, stop and have the valve body, overflow and mounting gasket assessed.
Why this mattersAn internal leak may originate somewhere other than the replaceable ring.
Path B: repair or replace the fill valve
Choose this path when the tank overfills or the inlet does not shut off after float adjustment, with an outlet leak ruled out. A healthy valve does not need replacement just because you can hear it.
Repair first, when supported: look up the exact valve’s maintenance procedure. Some have a replaceable seal or a removable cap for clearing sediment. Close the supply before opening anything. If the maker specifies a brief purge, shield the opening as directed and restore flow only for that controlled step. Never remove a cap with the supply on, and never guess a cap-release direction. Replace a cracked housing, unavailable service part, or valve that still fails to shut off.
- 01
Confirm access and shutoff
Read the new valve’s instructions completely. Find the supply coupling and separate mounting nut under the tank. If access is concealed, the connector is rigid or corroded, or the stop cannot shut off water, arrange help. Otherwise close the supply gently, flush and sponge the tank dry. Confirm no new water enters.
Why this mattersA fill-valve replacement opens the tank inlet; reliable isolation is essential. - 02
Catch water and disconnect the connector
Place towels and a small bucket under the inlet. Loosen the supply coupling at the bottom of the fill valve, by hand if designed for it. Use a tool only where its manufacturer permits. Keep the wall stop and pipe from twisting. Residual water may drain from the hose.
Why this mattersA moving wall connection or forced brittle coupling can cause a supply-side leak. - 03
Remove the mounting nut and old valve
Support the old valve inside the tank while removing its separate locknut underneath. Lift the valve out and remove the old sealing washer. Wipe the porcelain around the hole gently. Stop if you find a crack or chip that affects the seal.
Why this mattersA clean mounting surface helps the new washer seal without excessive tightening. - 04
Set height and fit the new washer
Install the supplied shank washer in the orientation shown in your valve’s instructions; do not reuse the old one. Adjust and lock the valve height before mounting when required. Check lid clearance, free float travel and the maker’s critical-level requirement. For Fluidmaster 400A-style installations, the molded C.L. mark must be at least 1 inch above the overflow top. The cap top is not the C.L. mark.
Why this mattersWaterline, valve height and back-siphonage protection are related but different settings. - 05
Seat and secure the valve
Insert the valve through the inlet hole, orient the refill outlet for a clear hose path, and fit the supplied mounting nut. Tighten exactly as directed. Many plastic nuts are hand-tighten only; do not add a routine quarter-turn with pliers. Do not use force to flatten or crack porcelain.
Why this mattersThe washer provides the seal. Extra torque can strip plastic or damage the tank. - 06
Reconnect the supply without sealant
Inspect the connector’s sealing washer and threads. Fit a compatible undamaged connector, starting the coupling by hand so it does not cross-thread. Follow its tightening instructions. Standard washer-sealed toilet connections do not need thread tape or pipe dope; do not reuse a damaged washer or add a second one.
Why this mattersThese fittings seal at the washer, not by packing the threads with tape. - 07
Route the refill tube correctly
Connect the hose to the fill-valve outlet and secure the supplied clip above an open overflow tube. Aim the stream into the opening; keep the hose end out of the tank water and do not push it down the tube. Leave an unobstructed path without a kink or a loop that catches the float. A dedicated canister port uses its own model-specific adapter or connection.
Why this mattersIncorrect hose placement can siphon tank water and create repeat refill cycles. - 08
Restore water and set the tank level
Open the supply slowly while watching every disturbed connection. Shut it back off if anything drips. Set the tank to the toilet’s waterline using the valve’s adjustment mechanism. Confirm the valve stops and water does not flow over the overflow rim. If the float reaches shutoff but water keeps entering, service or replace the valve rather than raising the overflow.
Why this mattersAn appropriate fill level supports the intended flush without continuous overflow. - 09
Set bowl refill and run the final checks
If the valve has an adjustable bowl-refill control, calibrate it according to its instructions and the toilet’s normal bowl level. Flush several times and verify consistent bowl refill, free float movement and complete inlet shutoff. Use a dry tissue on connections and repeat the dye test. Recheck later the same day.
Why this mattersA quiet tank alone does not prove the bowl is refilling correctly or the connector is dry.
The victory lap: quiet, dry, repeatable
Before replacing the lid, make sure the repair works more than once.
- Flush two or three times and wait for a complete refill each time. The handle, chain, flapper or tower and float should all move freely.
- Confirm the tank stops at its specified waterline below the overflow rim. There should be no continuing inlet flow after the refill has finished.
- Check that the bowl returns to its normal water level. Low bowl water after valve replacement often points to a disconnected or under-adjusted refill hose; do not solve it by overfilling the tank.
- Dry the supply coupling, valve shank, tank underside and wall stop, then use fresh dry tissue to detect moisture. Watch during refill and after shutoff.
- Run the no-flush dye test again and flush out the color afterward. Listen for unwanted refill cycles later that day.
- Refit the lid carefully and check that it does not touch the valve. Keep packaging, the model number and a photo of the finished installation for next time.
Still running? Use this comeback checklist
A new part is not a guarantee that you replaced the leaking part. Return to the observed water path.
| What you notice | What to check | What to do |
|---|---|---|
| New flapper, same leak | Part fit, hinge arrangement, chain tension, loose chain tail, seat condition and adjustable setting. | Correct fit and travel. A cracked seat, overflow tube or leaking flush-valve mounting gasket may require a larger repair. |
| New valve, repeated ghost refill | Tank-level loss, outlet seal and a refill hose pushed into the overflow. | Correct hose routing and repeat the dye test. Replacing the inlet does not repair an outlet leak. |
| Tank spills over the overflow | Float setting, interference, unlocked height adjustment and debris in a serviceable valve. | Use the model’s setup and service instructions. Stop if the inlet will not close reliably. |
| Weak flush or having to hold the handle | Chain slack, flapper fit and adjustable setting, tank waterline and bowl refill. | Restore the specified settings. If the bowl drains slowly or other fixtures gurgle, investigate a drain issue instead. |
| Whistle, slow refill or new chatter | A kinked connector, supply stop position or model-specific inlet debris. | Open a working stop normally without forcing it and follow the valve’s cleaning procedure. Repeated noise or pressure symptoms need assessment. |
| Water appears around the base | Whether it is supply water, tank leakage, condensation or leakage during a flush. | Stop and isolate safely. A floor or base leak is not diagnosed by the flapper test. |
Keep the quiet going
Treat the tank as a small mechanism, not a chemical bucket.
- Avoid drop-in tank tablets containing bleach or chlorine when the toilet or part maker warns against them. Concentrated cleaners can damage seals and affect warranties. Use approved cleaning methods and never mix cleaning chemicals.
- Check for silent toilet leaks periodically; EPA suggests at least annually. Also check after a new noise, unexplained water-use increase or a repair.
- In hard-water areas, inspect for deposits and use only model-approved cleaning methods. Do not sand sealing surfaces or attack them with harsh cleaners.
- Keep the supply connector visible and clear of stored items so new moisture is easy to spot. Inspect older stops and connectors before the next repair.
- Replace seals based on condition and performance, not an assumed universal lifespan. Water chemistry, cleaners, use and material affect service life.
Good questions, straight answers
The things people usually ask once the lid is off.
Should I replace the flapper and fill valve together?
Not automatically. If the tank loses water through the outlet but the fill valve stops reliably, a matched flapper or seal may be enough. Replace both only when diagnosis or their condition supports it, and make sure each part fits.
Can I replace these parts without removing the tank?
On many accessible gravity toilets, yes. A flapper usually comes out from above; a fill valve uses a nut below the tank. Replacing the entire flush valve, its mounting gasket or inaccessible hardware is a different job and may require tank removal.
Does a running toilet mean a bad fill valve?
No. A leaking flapper can lower the tank water and trigger a healthy fill valve. Watch the overflow and use a dye or isolated water-level test before buying an inlet valve.
How much slack should the chain have?
Enough for the flapper to sit flat while still lifting fully when the handle moves. Follow your part’s directions; one or two loose links is common. Avoid a universal half-inch measurement and keep the loose tail out of the seat.
Can I use petroleum jelly, glue or tape to seal a flapper?
No. Those are not a durable repair and may damage the rubber or foul the mechanism. Clean a sound seat gently and fit the correct replacement seal.
Is the water in the tank safe to touch?
It starts as supply water, but standing tank water and internal surfaces are not drinking-water clean. Wear gloves if desired, avoid contact with cleaning chemicals, and wash hands afterward. Never use tank water for drinking.
Is it okay to leave the supply off overnight?
If the stop closes reliably and is not leaking, isolating an internal tank leak can be temporary containment. The toilet cannot refill normally. Tell household members it is out of service and arrange the repair; do not rely on a leaking or seized stop.
Why is my new fill valve making some water flow at its base?
Some designs intentionally discharge into the tank at the base or other openings during refill. Check the model’s manual. Water outside the tank, or continued flow after shutoff, needs attention.
How much water or money will this save?
That depends on the leak rate, hours of leakage and your utility’s billing rules. A small silent leak and a wide-open flapper are very different. Compare meter or utility use before and after repair; no single gallon or dollar claim fits every toilet.
What if I have a pressure-assisted, concealed or smart toilet?
Use its exact service instructions and manufacturer support. A pressure vessel, inaccessible tank or powered system changes the procedure and parts. Do not apply a standard gravity-tank repair by guesswork.
When should I call Nothing But Sewer and Drains?
Call when the supply cannot be safely isolated, porcelain or valve-body parts are damaged, connections leak externally, access is difficult, or a correctly fitted repair still fails. Share the model number, symptom, photos and tests already completed. The team can discuss availability and scope.
Check the result.
If it improved
Keep the model number and repair photo. Recheck connections later that day and check for silent leaks periodically.
If it did not
Call with the toilet model, where water moves or leaks, and which tests or parts you tried. Leave the supply off if there is an external leak and it can be isolated safely.
Source guidance
These public resources informed the safety boundaries and general steps. The exact equipment and conditions at your property may differ.