What is this? Septic tank related

Where do i start? I'm basically writing on behalf of my parents.

For as long as i can remember we have had an issue with this Drain looking thing in our laundry room. What happens or used to happen as we now walk on egg shells when dealing with water in our house. The drain would back up and over flow into the laundry room from water from the septic tank? How do we know its from there? well the horrid smell that fallows it. It would happen randomly usually after laundry was ran or a few showers were taken within a few hours.

This drain thing always seems to have water in it, maybe 7-8 inchs below the hole, at all times, doesn't flucuate though.
The drain is maybe a couple feet higher than the tank sits. And its maybe about 40-50ft away.

We had pro's come out and blow the system out and try to figure out what was going on, had the tank pumped a few times maybe thinking it was full but found it wasn't. We though never figured out what this drain/breather tube thing was. Here are some pictures. Can anyone give us some sort of idea what this is and maybe some help in how to stop this?

Is there a lot of water coming out or just a bit? Could it just be the water you see 7-8 inches down being forced out? If so then the drainage system may be venting through there, indicating a blockage in your ventilation elsewhere. This should be investigated

Do you ever use the drain? If not you could always fill it in. Use a proper temporary drain bung first, and leave it in there for a couple of weeks. Pay attention to the performance of your drains, if they don't perform any differently it's probably safe to fill it in.

is it the lowest point of your property?i take it this is in your basement. Its a floor drain which there is a gully trap underneath (which is the water you say you can see from the hole) This drain line would normally run into your main line straight into your septic tank.
Best course of action would be to get your main line camera surveyed from your septic tank up the main line, to check for any roots or damage that is causing the system to back up.