1. Stir the rice flour and tapioca starch together and set aside. Bring the water, milk, butter, sugar and salt up to a boil in a medium saucepot. Add the rice flour mixture and stir vigorously with a wooden spoon until the dough “cleans” the pot as you mix it, about 90 seconds (the dough will be tight). Remove the pot from the heat and scrape it into a mixer fitted with a paddle attachment or using electric beaters, and beat the dough for 2 minutes to cool it down slightly.
2. Break the eggs into a bowl and add them one at a time to the dough as it mixes, waiting until each egg is incorporated before adding the next. Once all of the eggs are incorporated, spoon the batter into a piping bag fitted with a large star tip.
3. Pipe doughnut-shaped crullers onto a parchment lined baking tray and chill for 20 minutes or long enough so that they can be peeled off of the paper.
Preheat a tabletop fryer, or a deep pot filled with 2 inches of oil, to 375ºF. Carefully drop the chilled crullers into the fryer and cook for 2 minutes on each side, then remove onto a cooling rack over a tray to cool. Dust with icing sugar before serving.