I don't want to get into the dual flush question, but I will make some comment about Kohler. There seems to be a great many problems with Kohler. They make many models of toilets that do not use commonly available repair parts. You have to buy for Kohler and the repair parts often are as much as a good toilet. There also seems to be quality issues with Kohler, both in the manufacturing and in the performance. Frankly, you can do much better. I would suggest you serious look at the Toto brand linked from the home page of this forum. There seems to be absolutely none of the quality or performance issues with any of the Toto models.