There are different configurations.
Drains in an external box with an internal box that are connected with a bulkhead through the side of the tank.
Drains in a tall overflow with the pipes entering from the bottom.
Drains connected directly to holes in the side of the tank. This can be with a inner box or without one.
They all work the same way though it may not look like it.
In your first vid here is an external overflow box with pipes coming in the bottom.
The last one is a direct tank connection. All three pipes have valves so you can turn it completely off.
The risers above the tee are to vent air. Not needed with an overflow box. The top is open.
The middle pipe is the second drain. The middle height pipe.
The right pipe is the full siphon drain. It is vented but notice the red pipe. That is an air vent but once the water in the tank rises above it no air can enter and it is blocked. This is the lowest drain. The left pipe is higher and is the emergency drain. It is the highest.
This picture is not how a bean animal is usually used. There is usually more separation in height between them.
Here is the extremely simplified version.
The water entry level in the right pipe is the end of the pipe. This is the full siphon drain.
The water in the secondary drain starts down when water rises above the center of bottom curve in the pipe. The top has a small vent hole to vent air.
The third emergency drain is dry in the center.
But there is no need for the curved pipe on the right. Just the end of the bulkhead is fine. The only time this pipe is needed is if your box is shallow enough that the drain can suck a vortex down to the drain and suck in air. Then the curved pipe prevents that.
This is a very shallow box in the picture.
This is what I have on my 240 gallon. My 2 pipes in the center with valves have no pipes at all in them and both run full siphon all the time. A little water goes down the right pipe and that is the level in the box. The left is dry.
All you have to do if a vortex forms from the main drains is drop a 3/4 or 1 inch PVC tee in the box. Just laying in there, no connection. It makes enough turbulence that a stable vortex is never formed.
So unless your box is shallow all you need is some stand pipes of correct height and open bulkhead for the full siphon drains.
Pro Tip - when you cut the stand pipe cut the top at a slight angle instead of square. This way the trickle of water going down the secondary drain will always start at the lowest side and run quietly down the side of the pipe.
What you do at the bottom matters too. Full siphon drains have to push air out the bottom when they start so place the end of the drain just slightly under the water.
The one vented or open at the top dont care about the bottom much, BUT if something goes wrong the secondary may go full siphon too so I always place it the same way as the main drain, just under the water.
You never want drains to pump air. They will be noisy and unsteady.