Sure. There are pretty solid explanations of Bean Animal and this is my first, but this is my interpretation of it for my application.
The drain on the far right has the lowest inlet inside the overflow box. The job of this drain is to draw only water to the sump with a full siphon. This is great because it's the most efficient use of the drain, and because there is no air, it's also silent. The goal in theory is to balance the rate of flow through the full siphon drain to exactly match the flow of the return lines. For that reason, this drain is oversized and has a gate valve which can be tuned to reduce the flow rate to exactly match. In practice though, these flow rates won't ever match. The full siphon drain will always be a little too fast or a little too slow which would, left to its own devices, eventually drain or overfill the overflow box. The full siphon drain needs some help.
For this reason, the full siphon is backed off slightly such that it handles almost all of the return flow. This causes the water level in the overflow box to rise slowly. In the overflow box, the open channel drain inlet is placed above the full siphon to pick up the slack. It has an open inlet, which allows both air and water to enter the drain line freely. When tuned correctly, this drain line only has to handle a slight trickle of water, which is the the flow rate of the returns minus the flow rate of the full siphon; that tiny difference that was created by backing off the flow capacity on the full siphon gate valve. Because this is a small amount of water, it doesn't surge or interact with air as it flows and generally hugs the edges of the drain due to surface tension. This results in a nearly silent open channel drain. But what happens if this drain gets clogged? The open channel needs some help.
The third is an emergency drain, the purpose of which is to move water to the sump in the event that the lower drains become clogged, or there is a temporary increase in water level. For this reason, it has the highest inlet in the overflow box just above the open channel. Oftentimes, this drain's outlet is placed high in a main sump chamber so that when it's in use, it causes a ruckus so the reefer knows that the drains are not operating normally. Under normal circumstances, this drain is not in use and doesn't have any effect on noise. This leaves us with a system that handles the precise amount of flow without variation, no noise, and enough redundancy to satisfy a NASA engineer.
