The Short Answer
Put one drop of food coloring in your toilet tank. Wait 15 minutes. If color appears in the bowl, the toilet is leaking and should be repaired. The test is free and takes 15 minutes.
It happens to all of us. Even me.
I had brand new cesspools put in around 2000. I just had the main pool pumped a month ago, for no reason other than to finally get it emptied again.
Then some family members living in my apartment didn't tell me my toilet was running.
By the end of the weekend I had two full cesspools and nobody available to pump them out. On my own property. As a plumber.
A running toilet doesn't sound like an emergency. It doesn't flood anything. It doesn't make much noise. But it can move hundreds of gallons of water a day straight into your system, and if you're on cesspools, that water has to go somewhere.
Here's the test. It takes fifteen minutes and it costs nothing.
Put one drop of food coloring in your toilet tank — the tank, not the bowl. Walk away. Come back in fifteen minutes and look in the bowl. If the water in the bowl has picked up that color, water is leaking through from the tank, and your toilet is running whether you can hear it or not.
If it's colored, call a plumber and have the toilet fixed. That repair is a fraction of what it costs to have a cesspool pumped, and it saves an enormous amount of water besides.
Do it in every bathroom in the house. It's the cheapest fifteen minutes you'll spend all year.
Common Questions
How much water does a running toilet waste?
A running toilet can waste 200 to 400 gallons a day depending on how bad the leak is. Over a weekend that's enough to fill a cesspool. The flapper is the most common culprit — it's a $10 part that takes five minutes to swap, and it saves you thousands of gallons.
Why does a running toilet fill a cesspool?
Every drop that goes through the toilet goes into your septic or cesspool system. A running toilet sends a constant stream of clean water into the tank that never stops. The system can't drain fast enough, and it backs up. On municipal sewer it's less dramatic but you're still paying for every gallon on your water bill.
Can I fix a running toilet myself?
Sometimes. If the flapper is worn out, that's a simple swap anyone can do. If the fill valve is the problem, it's a bit more work but still doable with a kit from the hardware store. If you've done the food coloring test and you're not sure what's leaking, call a plumber — it's a quick, inexpensive repair.
Have a question about your own house?
I talk to every customer myself. Call the shop and ask.