I Thought My Toilet Tank Was Cracked, but the Leak Was Coming From Somewhere Else
When I first saw water collecting under my toilet, I assumed the tank was cracked. The floor stayed damp, water kept reappearing after flushing, and nothing looked obviously loose. Because the toilet had been worked on recently, my next guess was the fill valve.
Both assumptions were wrong.
Why it looked like a cracked tank
The leak wasn’t dramatic. There was no steady drip, just water slowly appearing under the toilet after use. The tank felt damp, the floor stayed wet, and everything pointed to a hidden fracture or internal failure.
Cracked porcelain felt like the only explanation.
What I checked first
I ruled out the obvious:
- no visible cracks in the tank
- no water overflowing inside the bowl
- no constant running
The fill valve looked fine. Everything inside the tank behaved normally.
That’s when I called a plumber.
What the plumber actually found
The issue wasn’t the tank or the valve. It was the plastic sealing ring on the water supply hose.
The hose itself was new, installed during a recent plumbing visit, but the plastic washer inside the connection was cracked. Under pressure, it allowed small amounts of water to escape every time the toilet refilled.
That water ran down the back of the toilet and pooled on the floor, making it look like a tank leak.
Why this is easy to miss
A cracked washer doesn’t leak constantly. It leaks under pressure. That’s why:
- the floor gets wet after flushing
- the tank looks damp
- the leak seems to come from nowhere
Because the part is hidden behind the toilet, it’s easy to blame the tank or internal components instead.
The fix
The plumber replaced the cracked plastic ring with a new one and reseated the hose correctly. That was it.
- No new tank.
- No new valve.
- No ongoing leak.
What happened after
The floor stayed dry. The tank stopped feeling damp. The water didn’t come back.
Nothing else changed. The toilet didn’t change. The cleaner didn’t change. The seal did.
When this applies to you
This is worth checking if:
- the toilet was recently installed or serviced
- water appears only after flushing
- you suspect a cracked tank but can’t see one
- the leak seems to come from behind the toilet
Before replacing anything major, check the supply hose connection and the washer inside it.
What I do now
I keep an eye on that connection whenever plumbing work is done. A tiny plastic ring caused a problem that looked far bigger than it was.
Sometimes the leak isn’t the toilet. It’s the smallest part you never see.