some toilets rely on water height above the bowl for “pressure ” .434 times the height and the volume inside the holding tank.
Some toilets rely on water Pressure min of 25 PSI and a flow rate of 1.6 – 3.5 GPF
Navel flushometers rely on low pressure BUT use hydraulics for a flush.
The sloan flushmate relies of Air pressure with a very small amount of water 1.6 Gallons
The old high tank was nothing more than on Oak box with a copper lining that used gravity for the flush as this tank was normally hung around 8 ft above the toilet bowl bowl… Then there is the Gas Fired toilets that use NO WATEr but a gas flame to get rid of well for that you can look into the AGE code.
When you analyze the construction of a toilet, you will see that it is nothing more than a fancy syphon. As such, the water from the flush is used to start the syphon functioning, and then to add enough additional water to scour the inside of the bowl and replace the water that is “sucked out” of it. Each type of bowl uses its own method of starting the syphon, from the “brute force” of a washdown toilet that just overwhelmed the syphon with a large amount of water, to the pressure assist Flushmates that create a venturi effect to start the action.
From what I understand, the USA small flush WC doesn’t work. You need a mate in Canada or here in Australia to send you one that does flush using a 6/3litre dual flush cistern, with out using a power assisted unit …… or a plunger