My pool has no main drain. This makes pumping out the pool to lower the water for the winter a problem.
I tried using a vacuum head connected to the skimmer, but there was enough air leak around the hose in the skimmer that the pump started sucking air when the water level dropped below the skimmer. So, I bought a small submersible pump to lower the water level for the winter. The pump is slow -- it takes about six hours to lower the water level to 18" below the coping.
This year a came up with a faster way. With the pool full, I hooked up the vacuum head and switched the multiport valve to "Waste" as I've done in past years. I also put the submersible pump in the shallow end, placed the end of the hose from the submersible pump in the skimmer, and turned on the submersible pump. I then turned on the main pump.
The submersible pump kept enough water into the skimmer to keep air from getting into the hose connected to the main pump. By using the main pump, I was able to drop the pool level in about an hour. After I saw all was working well, I did a final vacuuming before closing the pool while doing the pump down.