I think the one way valve would be needed to make sure all of the water is consumed. This explanation sees to make sense to me. The water flows up the white tube and is dispersed to drip evenly on the waiting coffee grounds.What happens next is exactly what happens in a typical aquarium filter: The tube is small enough and the bubbles are big enough that a column of water can ride upward on top of the bubbles. When the water boils, the bubbles rise up in the white tube.
When you turn on the switch, the resistive heating element starts heating the aluminum tube and eventually the water in the tube boils.This all happens naturally because of gravity. Then the water flows through the one-way valve, into the aluminum tube in the heating element and then partially up through the white tube.
