That hiss you keep hearing at night
If you live in Republic and you've noticed the toilet tank refilling itself every twenty minutes or so, sometimes with a faint hiss, sometimes with a full running sound, you're not imagining it. It usually happens most at night when the house is quiet enough to hear it. That sound is water leaking from the tank into the bowl, slowly, and it's almost always the flapper.
A lot of homes in Republic and the surrounding area, whether they're the older ranch houses near downtown or the newer builds out toward the edges of town, have toilets running on parts that are ten, fifteen, twenty years old. Flappers are rubber, and rubber doesn't last forever. It hardens, it warps, it stops sealing.
The dye test, done right
The classic way to confirm it's the flapper is to drop a few drops of food coloring into the tank, wait about fifteen minutes without flushing, then check the bowl. If color shows up down there, water is getting past the flapper seal. It's a simple test and it costs nothing, but people mess it up in a couple of predictable ways.
First, don't flush during the wait. Sounds obvious, but if someone in the house uses that bathroom during the test, you've got nothing. Second, give it the full fifteen minutes. A small leak might not show color in five. Third, look at the water in the bowl before you start, some well water and municipal water in this area has a slight tint already, so know your baseline.
More on this from The Flapper Test That Settles A Running Toilet.
What the flapper actually tells you
Once you've confirmed a leak, open the tank lid and actually look at the flapper while the toilet is at rest. You're checking for a few things: is it sitting flat and centered over the flush valve opening, is the rubber cracked or slimy, does it feel stiff instead of pliable, and is the chain connecting it to the flush handle too tight or too loose.
A chain that's too short can hold the flapper open just slightly, which is enough to cause a slow leak that mimics a bad seal even when the rubber itself is fine. This is worth checking before you buy a replacement part, since it costs nothing to adjust a chain link and see if the problem goes away.
Hard water is common in this part of Missouri, especially for homes on well water outside town, and mineral buildup on the flush valve seat is something people miss. Even a brand new flapper won't seal against a ring of grit and scale. Wipe the seat clean with a rag before you decide the flapper is the culprit.
Seasonal wear you might not expect
Republic gets real winter cold and real summer heat, and that swing does something to toilet parts that people don't think about. In an unheated crawlspace or a toilet in a rarely used guest bathroom, especially in an older farmhouse-style home, the tank water can run colder in January, and rubber contracts slightly in the cold. That can make a marginal flapper seal worse in winter and seem to improve a bit in summer, which throws people off when they're trying to diagnose it.
Homes built before the 1990s in the Republic area often still have the original ballcock-style fill valve and a flapper that's been swapped once or twice over the decades, sometimes with a part that doesn't quite match the flush valve. A universal flapper from a hardware store shelf isn't always a perfect fit for an older Eljer or American Standard toilet common in this area's older housing stock. If the replacement still leaks after a fresh install, mismatch is a likely reason.
When it's more than a flapper
If you've replaced the flapper, cleaned the valve seat, and adjusted the chain, and the toilet is still cycling on its own, the problem may have moved past a simple parts swap. A flush valve seat that's cracked or corroded won't seal against any flapper, no matter how new. That means pulling the tank off the bowl, which is more involved and easy to get wrong if you've never done it, since the tank bolts and gasket have to seat evenly or you'll trade a running toilet for a leaking one at the base.
This is also the point to call someone if your water bill has been climbing for a couple of months and you can't pin down the cause, or if you've got an older toilet where parts don't match anything sold locally anymore. A running toilet wastes a genuinely large amount of water over a year, more than most people guess, so it's not a problem to let sit once you know it's there. But there's no shame in doing the dye test and the visual check yourself first. That part is quick, cheap, and tells you exactly how far the problem actually goes.