There’s a greedy cup siphon in your washing machine fabric softener try. Also called a Pythagorean cup. It’s also used in urinals and novelty drinking receptacles. It’s an example of a fluid dynamic mechanism.
source/image: Steve Mould
The fabric softener tray in a top-load washing machine operates by utilizing a Pythagorean siphon to distribute fabric softener diluted with water across the clothing in the washing machine. A Pythagorean siphon is composed of 4 chambers with 1 chamber in the center that liquids can escape through.
As liquid fills up the 4 chambers, the pressure acting on the liquids remains constant and so the level of liquid in each chamber remains the same. Once the liquid reaches the top of the Pythagorean siphon it begins to escape through the central chamber as the effects of gravity take hold.
As this process happens, the liquid from both two chambers next to each side of the central chamber forms a seal above the central chamber due to the surface tension of the liquids. Due to this seal, air can then not escape through the central chamber, so the weight of the water in the central chamber forces all the remaining liquid in every chamber to pour out of the Pythagorean siphon. This technology is utilized in the fabric softener tray of a top-load washing machine.