What’s inside a hut of a sewer vent chimney pipe?

The vent pipes allow the sewer gases to escape to the outside, rather than being released inside the house. As mentioned, the air pressure in sewer pipes is the same up and down the length of the pipe. But when water moves through the pipe, it compresses the air ahead of it, creating a positive pressure.

You're obsessed with this.  Please see a shrink.  They should be included with your healthcare.

It's an electric pump, necessary electrical equipment for said pump, lighting, monitoring equipment, power outlets and security systems.

There are various valves and tanks for the sewage.

https://youtu.be/Z9-DXl028-Y

Nothing. Just adequate working space for a maintenance engineer.