What you need
- Supplies
- Food coloring (a dark color works best), a towel, a pen
- Time
- About 20 minutes per toilet, mostly waiting
- Rule
- Do not flush during the waiting period
- Clean-up
- Flush afterward; food coloring does not harm the toilet
Running the test
Let the tank fill completely
Wait until the fill valve has shut off and the tank is quiet.
Lift the lid carefully
Set it on a towel on the floor. Tank lids crack easily if dropped.
Check the overflow first
Look at the overflow tube. If water is already trickling into it, note that: the fill valve level is the problem, not the flapper.
Add the dye
Put several drops into the tank water, not the bowl. Put the lid back on.
Wait and check the bowl
After 15 to 20 minutes, look in the bowl. Any color means water passed the flapper.
Results
| Toilet | Date | Water in overflow tube? | Color in bowl? | Next step |
|---|---|---|---|---|
| Yes / No | Yes / No | |||
| Yes / No | Yes / No | |||
| Yes / No | Yes / No |
What the result means
- IfNo color in the bowl and no water in the overflow tubeThenThe tank is holding water; look elsewhere if the toilet still runs.
- IfColor in the bowlThenThe flapper or the flush valve seat is leaking; a new flapper is the usual first step.
- IfWater spilling into the overflow tubeThenLower the float so the water stops below the top of the tube, or replace a worn fill valve.
- IfColor returns even after a new flapperThenThe flush valve seat may be scaled or pitted; ask a plumber to look.
Before calling a plumber about a running toilet
- Record the dye test result for each toilet.
- Note whether the shutoff valve closes fully.
- Take a photo of the inside of the tank.
- Note the brand or model printed inside the tank if visible.
Common questions
Can food coloring stain the toilet?
It normally flushes away. Flush once after the test so it does not sit in the bowl.
Can I use something other than food coloring?
Some toilet parts come with dye tablets for the same purpose. Any dye made for toilet testing works.
The test was clean but the toilet still runs. Why?
The fill valve may not be shutting off fully, or the water level may be set into the overflow tube.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.