So your toilet won’t stop running. That sound like water quietly trickling 24 hours a day is one of those things that starts small and somehow gets more annoying every single day.

Here’s the thing most people don’t know: a running toilet wastes up to 200 gallons of water a day. That’s real money disappearing every month. And in most cases, the fix costs $4 and takes about 20 minutes.

I fixed mine last winter. Bought a replacement flapper at the hardware store, swapped it out before lunch, and the sound was gone. Here’s exactly what I did.

Step by Step:

Step 1: Open the tank and listen

Take the lid off the back of the toilet the tank, not the bowl. Set it somewhere safe. Now watch what’s happening inside. Is water trickling over the top of the tall tube in the middle? That’s the overflow tube, and it means your water level is too high. Is the water level fine but you can hear trickling into the bowl? That’s a leaky flapper. Most running toilets are a flapper problem.

Step 2: Do the food coloring test

Not sure which problem you have? Drop 5 or 6 drops of food coloring into the tank. Don’t flush. Wait 15 minutes. If color shows up in the bowl without flushing, your flapper has a slow leak. This catches silent leaks that waste water without making obvious noise. A lot of people have this and have no idea.

Step 3: Turn off the water and drain the tank

The shut-off valve is on the wall behind the toilet near the floor. Turn it clockwise until it stops. Then flush the toilet. Most of the water will drain out. Sponge up whatever’s left you want the tank as dry as possible before working in it.

Step 4: Replace the flapper

The flapper is the rubber seal at the bottom of the tank. It’s usually connected by two little loops to pegs on either side of the drain, and attached to the flush handle by a chain. Unhook the loops, unhook the chain, and take the old flapper to the hardware store to match the size. Snap the new one on, reconnect the chain with about half an inch of slack, and you’re done with the hard part.

Step 5: Adjust the float if the water level is too high

If water was going over the overflow tube, the float needs to come down. On modern toilets there’s a small adjustment screw or clip on the fill valve. Turn it to lower the float until the water stops about an inch below the top of the overflow tube. On older ball float toilets, you can gently bend the arm downward.

Step 6: Turn the water back on and test

Slowly open the shut off valve. Let the tank fill. The filling should stop on its own. Flush once and watch the tank should refill and then go quiet. If it’s still running, double check that the flapper is sitting flat on the seat and the chain isn’t caught underneath it.

Quick Tips

When you buy a new flapper, get a universal one unless your toilet is a specific brand that uses proprietary parts. Korky and Fluidmaster both make reliable universal flappers for about $3 to $5.

If you’ve replaced the flapper and the toilet still runs, the flush valve seat (the ring the flapper sits on) might be worn or warped. Run your finger around it if you feel roughness or a groove, the seat needs to be replaced or the whole flush valve assembly needs to go.

A running toilet is one of those repairs that seems like it should require a plumber. It almost never does. A $4 flapper and 20 minutes of your time is genuinely all it takes in 90% of cases. Fix it this weekend.