Symptoms
- Visible crack line on the tank exterior or interior
- Water seeping out along the crack, especially after flushing
- Puddling behind or beside the toilet
- Crack may have appeared after tank lid was dropped or the tank was overtightened
Likely causes
- CommonImpact damageDropping the lid, bumping it hard, or leaning on the tank can crack the porcelain.
- CommonOvertightened tank boltsCranking the bolts too tight when reassembling can stress and crack the porcelain around the bolt holes.
- PossibleAge and stress crackingOld porcelain can develop hairline cracks over years from repeated temperature changes and settling.
What to do
- Turn off the water supply at the shutoff valve right away to limit water loss.
- Dry the area and confirm the crack's exact location and how much it's leaking.
- Do not use the toilet until it's repaired, since pressure from flushing can worsen a crack.
- A small hairline crack away from stress points may sometimes be sealed temporarily with a waterproof epoxy made for porcelain, as a stopgap only.
- Plan on tank replacement for any crack near a bolt hole or a crack that's actively leaking, since these tend to worsen with use.
Tools and parts
- Towels
- Waterproof porcelain epoxy (temporary only)
Replacement toilet tankSearch: “toilet tank replacement for [your toilet model]”
When to call a pro
Call a plumber to replace the tank, especially if the crack is near a bolt hole or growing, since a full tank failure can cause significant water damage.
Safety
Use caution
Shut off the water supply immediately and avoid using the toilet until the crack is properly repaired to prevent a sudden bigger leak.