Interactive Photo Diagram
How a Toilet Works
A look inside the tank — most toilet problems happen here, and you can see everything by removing the lid.
Reference checked: component relationships and terminology were reviewed against manufacturer documentation from KOHLER. This is original Classic Plumber educational artwork, not a manufacturer drawing.
Tap a numbered marker to learn what that part does.
Overview
A toilet is simpler than it looks. The tank stores water for a flush, the bowl holds water to seal out sewer gas, and the flush mechanism lifts a flapper to let water rush from the tank into the bowl. Almost every toilet problem — running, weak flush, phantom refills — traces back to a few parts inside the tank.
How It Works
When you press the handle, the lever lifts the chain, which lifts the flapper. Water rushes from the tank through the flush valve into the bowl, carrying waste down the drain. As the tank empties, the flapper drops back over the flush valve to seal. Meanwhile, the fill valve — triggered by the dropping water level — opens to refill the tank. When the water reaches the set level, the fill valve shuts off. If any part of this cycle fails, you get a running toilet, a weak flush, or a phantom refill.
Key Components
Fill Valve
Refills the tank after a flush and shuts off when the water reaches the right level.
Flapper
The rubber seal at the bottom of the tank. Lifts to flush, drops to seal.
Flush Valve
The opening the flapper seals. Water rushes through here into the bowl.
Overflow Tube
Prevents tank overflow — excess water runs into the bowl instead of the floor.
Handle & Trip Lever
The flush lever. Pulls the chain that lifts the flapper.
Chain
Connects the handle lever to the flapper. Needs slight slack to seal properly.
Shutoff Valve
On the wall behind the toilet. Turns off water to the toilet for repairs.
Supply Line
The tube from the shutoff valve to the bottom of the tank.
Common Issues
Running constantly
Worn flapper not sealing, or fill valve letting water overflow into the tube.
Read the guidePhantom refills
Slow flapper leak — water seeps into the bowl, level drops, fill valve tops it off.
Read the guideWeak flush
Partially closed shutoff valve, clogged rim jets, or low tank water level.
Won't flush
Broken handle, disconnected chain, or stuck flapper.
Maintenance Tips
- Check the flapper once a year — if it feels slimy or warped, replace it (a $5 part).
- Clean the rim jets (small holes under the rim) with a brush to maintain flush strength.
- Don't use chemical tablets in the tank — they degrade the flapper and rubber parts.
- Confirm the shutoff valve turns freely so you can use it in an emergency.