On 12/8/2010 11:12, David Nebenzahl wrote:

One weird thing, though: instead of being at the bottom of the tank like
you'd expect, the flapper sits a couple of inches up on an extension.
This is obviously by design. Seems strange to leave that much water in
the bottom of the tank; there must be some reason for this.
(Hydrodynamics?)

One possible benefit is that the cold fill water mixes with the more
tepid water reducing the likelihood of tank sweating.