Harry K wrote:
But really, when the flush valve opens, the pressure is not what
operates, it is the velocity of the water. The pressure is what gets
you the velocity. Thus it doesn't matter what the pressure in the
mains is, your tank height is all that counts. Even the "pressure
assists" operate the same way.

You don't have "pressure" unless the water is confined in something.


The water is confined by the orifaces in the toilet. Otherwise, it would drain
the tank a lot faster. Try flushing a tank removed from the toilet.

If there were no pressure, they wouldn't need a gasket between the tank and the
base.