My guess is that your toilet is a 1.6 gallon per flush model. (Having worked for a fixture mfg selling toilets for 15 years) This 1.6 technology is good except that EVERY toilet mfg uses a different flapper. The bowl is engineered as a 1.6 but the flapper is the metering device. (It's how long the flappper stays open.) The replacment parts in the market place have not adjusted to this. To fix ur problem u need to purchase a flapper specifically made for ur toilet. IE Kohler AM Standard Eljer etc. Find a plumbing wholesaler in your market that sells ur brandname & get the flapper from them.

It also helps to add tank stabilizers to the back of the tank that then attach to the wall behind the tank. These don't cost much as add much needed support when heavier users lean their backs against the back of the tank. Without the stabilizers, the tank loosens creating leaks or even breaking the tank. We install new toilets with stabilizers on every toilet we set. The stabilizers will also prevent the rocking of the tank that will ruin the tank donut (gasket).

I've had the same situation in the past. Just a tiny bit of water seen going into the toilet until the level in the tank gets low enough that it does a partial flush. I replaced the flapper 3 times made by different manufacturers before I found one with a perfect fit, that did not allow any water to leak. Have you tried different manufacturers for the flapper? Have you wiped the top of the pipe leading to the bowl where the flapper meets it? Might there be rust or hard water deposits on it? Sue

I went with the Toto Maris. Very small water spot - don't know if you can tell, but the water level is way down to where it flattens out, but might be something we could adjust? Anyway, we like it. Its comfortable, Sanigloss keeps it very clean. Planning to use the same one in our next remodel! Which Geberit tank are you planning to use?