Orca, good question and fair question.
ET hitches have leveling valve and were designed with one from day one (10 years ago). This has created two classes of people, "dumpers" and "non-dumpers", the non-dumpers being the ET owners. I have to spend considerable time with new ET owners to undo the dumper instincts, they are "powerful". Unfortunately there is no patch to deal with that addiction.
The non-dumper technique is pretty simple and "gentle" on the truck and trailer.
When positioned and ready to unhitch lower the fifth's jacks until they come in firm contact with the ground.
Lower the jacks (raise the fifth) a little more (1/4 inch or so) and listen to air hissing. The sources of that high pressurized air are twofold, the hitch suspension (air bags) and the truck suspension (air bags), after a minute or two the hissing will stop.
Raise the fifth another 1/4 inch and listen to the hissing air again, you might have to do it 2-3 times until the last time you raise the fifth you will hear no hissing and you will observe the the king plate has slightly separated itself from the top of the hitch head (there is a slight gap).
Open the jaws on the head and drive off☺️
You have just joined the ranks of "non-dumpers"
The whole concept involved here is this. By slightly raising the fifth you are removing the weight from both, the hitch and the truck, therefore both dump the air (automatically) to reach the "new" equilibrium (in the hitch and on the truck). By repeating this you eventually reach the point where there is no weight (from the fifth) on both the hitch and the truck. At that point there still will pressurized air in the hitch and in the truck but only enough to keep the truck and hitch level and not supporting the fifth any more. Therefore nothing will "jump up" when you drive off.
In my earlier post I mentioned the design of the bracket which you need to hold and position the valve, you see one holding the air valve in the above picture. Its height and location is not arbitrary for the system to work properly, quite a bit of thought went into this simple bracket.