[Wavery]

The amount of water that it takes to flush depends on how long you hold in the flush button. It doesn't have a fresh water "Tank", like your home toilet.

Your home toilet needs at least a gallon (or more) of water to get the refuse past the trap and into your sewer drain pipe.

The Elkmont toilet flushes directly into the holding tank so your only concern is to empty the bowl. That could take 1 cup of water if the bowl is clean to start with.

Here are a few tips for conserving flushing water:

Wax the inside of the toilet.
Wet the bowl before using.
Put a layer of TP on the bottom of the bowl before using.
You could also use teflon spray before using.

If you're careful, you should get 10-15 flushes from a gallon of water.