An unvented washer drain can cause problems for other fixtures.
In my brothers cabin, it caused the kitchen sink to back up with nice gooey stuff.
I have also seen washer hoses that were sealed to the drain.
To get it to drain right, I had to drill some holes in the plug.
They are right, don't seal it. They even make a fitting with small holes that clamp a hose to the drain for just that reason, you need some air movement.
You do need a trap, and a vent for it.
This isn't really new stuff here anymore. It's how it's done.
If you need more height, you can go with a basin and pump.
The washer has a pump, it would be adding one more to get the water up higher.
Here is a link on washer drains