Have I missed anything?

[expose]

Can't you pressurize your main drain line (from near the pump) until bubbles start coming out of the drain? Then turn off the valve.

If the drain line was properly installed, it should run downhill from the pump all the way to a low point, and then run uphill all the way to the drain. That means that once bubbles are coming out of the drain, the section between the pump and the low spot should be completely filled with air. (It should take about 5 psi to do that if the water is about 10 feet deep at the low spot) At that point, while it is still bubbling, turn off the main drain valve. In theory, air should remain in the line all winter if the valve and pipe don't leak.

I don't have experience with this, so don't take my word for it. I do intend on doing my pool this way unless somebody knowledgeable says that it's a bad idea. (Then I'd like to know what you're "supposed" to do.)

[Wolffe]

In my case, my main drain runs from the bottom of my pool to a second opening in my skimmer. My skimmer goes down below the current water level in my pool so as soon as I open the main drain, it starts filling the skimmer.

I suppose I could lower the water even further, pressurise the main drain, then raise the water level up a bit.

Can anyone tell me if this is necessary? I know the pool guy didn't do that.