Gravity-operated toilets are best used in houses that have low water pressure. Named so because it pressurizes the water when it is filling and rapidly releases the pressure when flushed. This causes the water to be forcefully pushed from the toilet. One possible drawback is that when it flushes it makes a loud noise. The increased pressure helps break up any debris in the pipe.
Prices range from the blue collar toilet to the royal throne.
You just need to choose the model type, color and shape that you want. Measure the distance from the wall to the pipe that is in the floor. Measure to the closest bolt if there are two. The customary distance is 12 inches but it could be more, or less. There are different types of ballcocks that you can get.