How do you fix a leaking toilet?

Hello, Here's a quick review of how the refill mechanism works. There's a big float inside, which is connected to a valve at the end of a water hose. Once you flush, the float will drop and water will flow in to fill the tank. As a result, the float will rise and will gradually increase pressure on the valve. The water flow will now get weaker. It should eventually stop when the float gets to a certain level. So now, after you basically know how it works, I'll mention a couple of reasons which may cause such malfunction.

1.The valve is made out of rubber, it may get worn with time and thus cause water to continue flowing, even if the float is high enough and the tank is full. In such a case an "emergency pipe" will drain the water down to the bowl (a leak).

2.Something may had got caught near the float, keeping it from going all the way up (Maybe even friction between the float and the tank). Water will keep getting in, and a leak will start.

In addition to what AlonB mentioned, if the handle isn't returning to the correct position, the chain between the handle lever and the flapper (valve) could be hanging up on something.  If someone worked on it recently, the chain may not be adjusted properly.  There's also the posibility that the handle itself is defective.  You really will have to take the tank lid off, flush the toilet a couple of times and watch the mechanism operate to figure out what's going wrong.  You may find that the problem is far more obvious than you think.

I have a Kohler low profile toilet that I have replaced ALL the working parts inside (new rubber seal, flapper & water regulator).  I have double-checked the seal and flapper for leaks but the toilet still slowly siphons out of the toilet.  I cannot hear any water nor see water coming into the bowl.  Where else can I check for leaks?  I am stumped!

Either tighten up the screw or replace it, and I would recommend toto toilets . Mine has served me well for 10+ years.