How to Fix a Toilet That Leaks from the Tank

Water leaking from the toilet tank can come from several different places. Finding the exact source is the key to fixing it correctly. Here's how to diagnose and repair each type of tank leak.

Step 1: Find the Source

Dry the outside of the tank completely with a towel. Then flush and watch carefully where water appears:

At the supply line connection (bottom of tank) — loose or failed supply line fitting
At the tank bolts (two bolts on the underside of the tank) — worn bolt washers or loose nuts
Between the tank and bowl — failed spud washer (large rubber gasket)
On the tank surface itself — condensation (not a real leak) or a cracked tank

Fix 1: Leaking Supply Line

Turn off the water supply valve
Hand-tighten the supply line connection at the tank bottom — sometimes this alone stops the leak
If still leaking, disconnect the supply line, wrap the threads with PTFE tape, and reconnect
Tighten snugly — don't overtighten plastic fittings

Fix 2: Leaking Tank Bolts

The two bolts that hold the tank to the bowl have rubber washers that deteriorate over time:

Turn off water supply, flush, sponge out remaining water
From inside the tank, hold the bolt head with a screwdriver
From below, tighten the nut with a wrench — alternate sides, snug but not overtight
If still leaking, the washers need replacement: remove the bolts, replace the rubber washers and metal washers, reinstall

Fix 3: Leaking Between Tank and Bowl

The large rubber spud washer between the tank and bowl has failed:

Turn off water, flush, sponge out tank
Disconnect supply line
Remove tank bolt nuts from below
Lift the tank straight up off the bowl
Replace the spud washer (the large donut-shaped rubber gasket on the tank outlet)
Reinstall tank, tighten bolts evenly, reconnect supply line

👉 The fill valve and flapper repair kit is a good time to replace internal parts while the tank is off.

Fix 4: Condensation (Not a Real Leak)

If the tank feels cold and water appears on the outside surface — especially in humid weather — it's condensation, not a leak. The cold water in the tank causes moisture from the air to condense on the outside.

Fix: Improve bathroom ventilation (run the exhaust fan longer), or install a tank liner kit to insulate the inside of the tank.

Fix 5: Cracked Tank

If you find a crack in the porcelain tank, the tank needs to be replaced. Hairline cracks can sometimes be sealed temporarily with epoxy putty, but this is not a permanent solution. A replacement tank for your toilet model is the proper fix.

Bottom Line

Most toilet tank leaks are fixed by tightening or resealing the supply line, tightening the tank bolts, or replacing the spud washer. Dry the tank, flush, and watch carefully to find the exact source before starting the repair.

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