A clear diagnosis saves time.

1. Dry everything. Use paper towels around the tank seam, bolts, and base. Note wet spots after 5–10 minutes.
2. Check the supply. Look at the 3/8" (10 mm) compression nut and braided line.
3. Dye test the tank. Add 5–10 drops of dye or food colouring. Wait 10 minutes. Colour in the bowl means a bad flapper or seat.
4. Flush and watch. If water seeps at the tank-to-bowl joint, suspect the gasket or bolts.
5. Water around the base after flushes points to a failed wax ring. If the floor is spongy, you may need flange repair.

Tip: Many contractors find a phone photo helps spot slow seeps. Take before/after photos for records.

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Safety, Shutoff, And Tools

Before you start, work safe and prevent damage.

• Turn the shutoff valve 1/4 turn clockwise to stop flow. Flush and hold the lever to drain the tank.
• Sponge or shop vac the last 1–2 cm of tank water.
• Place a towel or pan under the tank and valve.
• Tools: 10" adjustable wrench, slip-joint pliers, screwdriver, putty knife, hacksaw (if rusted bolts), mini-level.
• Parts you may need: 3/8" supply line (30–40 cm), universal flapper, fill valve, tank-to-bowl gasket, 2 tank bolts with rubber washers, wax ring (standard 1" or extra-thick 1.5").

How to Fix a Leaking Toilet: Inside the Tank

Most leaks come from the flapper, fill valve, or tank connections.

Replace A Worn Flapper (15–20 minutes)

1. Shut off water. Drain the tank.
2. Unclip the old flapper from the overflow tube. Remove the chain.
3. Clean the flapper seat with a cloth. No abrasives.
4. Install a matching or universal flapper. Set the chain with about 6–10 mm slack.
5. Turn water on. Dye-test again for 10 minutes. No colour in the bowl means you’re good.

Common mistake: Too-tight chains hold the flapper open. Leave slight slack.

Replace A Noisy Or Leaking Fill Valve (30–45 minutes)

1. Shut off water. Drain and sponge the tank.
2. Disconnect the 3/8" supply line at the fill valve shank.
3. Remove the locknut under the tank. Lift out the old fill valve.
4. Insert the new valve with the rubber seal. Set the critical level mark at least 25 mm above the overflow tube.
5. Hand-tighten the locknut, then add 1/4 turn with pliers. Don’t over-tighten.
6. Reconnect the supply line. Set water level about 12–25 mm below the overflow.
7. Flush-test three times. Check for drips at the shank and line.

Stop Leaks At The Tank-To-Bowl Joint (30–60 minutes)

1. Shut off water and drain.
2. Hold tank bolts with a screwdriver. Gently loosen nuts under the bowl with a wrench.
3. If corroded, cut bolts with a hacksaw. Remove tank carefully.
4. Replace the large tank-to-bowl gasket and both bolt sets. Rubber washer goes inside the tank, metal washer and nut go outside.
5. Set the tank back. Tighten both nuts evenly, alternating sides. Snug plus 1/4 turn. Do not crack the porcelain.
6. Refill. Check for weeping around the bolts and joint.

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Fix Leaks At The Base (Wax Ring)

If water seeps at the base after a flush, the wax ring likely failed.

1. Turn off water. Flush and sponge the tank and bowl dry.
2. Disconnect the supply line. Remove two closet bolt nuts.
3. Rock the toilet gently front to back. Lift and place it on a towel.
4. Scrape old wax from the flange and horn with a putty knife. Clean to bare surfaces.
5. Inspect the flange. If it’s below finished floor by more than 6 mm, use an extra-thick (1.5") ring or spacer.
6. Set a new wax ring centred on the flange. Align new closet bolts at 3 and 9 o’clock.
7. Lower the toilet straight down. Press with body weight. Don’t twist.
8. Install washers and nuts. Tighten each side evenly. Snug plus small turns until stable.
9. Reconnect the supply line. Turn on water. Flush-test five times. Dry-towel the base and check again after 10 minutes.

Pro tip: If floors are uneven, add plastic shims before final tightening. Caulk around the base front and sides, leave 50–75 mm gap at the back as a leak indicator.

Supply Line And Shutoff Leaks

Small drips add up fast. Fix them before they ruin cabinets or floors.

Replace A Dripping Supply Line (10–15 minutes)

1. Shut off water.
2. Unscrew the 3/8" compression fitting at the valve and the nut at the fill valve shank.
3. Install a new braided line. Hand-tight, then 1/4 turn with a wrench.
4. Dry with a towel. Check again after 5 and 15 minutes.

Service Or Replace A Sticky Shutoff Valve (20–40 minutes)

1. Try backing the packing nut off 1/8 turn. Close, then open the valve fully, and snug the packing nut.
2. If it still leaks or won’t close, replace the valve (angle stop). Shut main water if needed. Use two wrenches to hold back on the house side.
3. Reopen water slowly. Check for drips at 5, 10, and 30 minutes.

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Test, Clean Up, And Document

Testing proves the fix and reduces callbacks.

1. Dye-test the tank again. Wait 10 minutes.
2. Dry-towel all joints: shank, bolts, tank seam, base. Recheck after 15 minutes.
3. Flush five times. Watch for weeping at connections.
4. Level the tank and bowl if needed. A mini-level helps avoid stress on seals.
5. Caulk the base front and sides. Clean the area.
6. Document parts replaced and times: flapper (15–20 min), fill valve (30–45), tank gasket (30–60), wax ring (60–90). Photos help with warranty.

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FAQ

Why is my toilet leaking at the base only after flushing?

That’s a failed wax ring or a loose bowl. Water escapes only when the bowl dumps. Replace the wax ring, check flange height, shim if needed, and tighten nuts evenly. Always towel-test after five flushes.

Can I use silicone instead of a wax ring?

No. Silicone or putty won’t seal the waste horn and flange correctly. Use a standard or extra-thick wax ring, or a proven waxless seal designed for toilets. Caulk the base after the seal is set, leaving a small gap at the back.

How tight should tank bolts be?

Snug and even. Tighten both sides a few turns at a time. Aim for hand-tight plus about a 1/4 turn. Stop if the rubber compresses and the tank seats level. Over-tightening can crack the tank.

My tank refills slowly and I hear hissing. What’s wrong?

Likely a failing fill valve or debris in the valve. Replace the fill valve and set the water level 12–25 mm below the overflow tube. Also check the 3/8" supply line for kinks.

When should I replace the whole toilet?

Replace if the bowl or tank is cracked, the flange is severely damaged, or parts are obsolete. Also consider replacement for persistent clogs or if you want a 4.8 L/flush model to cut water use.

Conclusion

Fixing a leaking toilet comes down to finding the source, replacing the right part, and testing well. Most jobs use basic tools and common parts, and you can complete them in under 90 minutes. Next steps:

1. Diagnose: tank, base, or supply line.
2. Replace the failed part and re-test with dye and dry towels.
3. Document parts and time for warranty and billing.

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