Good idea on filling first.

I have an 18x36 IG with a solid cover (with mesh drain in the center) so the rain drains into the pool all year long. I have to pump water off constantly throughout the winter (usually 3 or 4 times, about 6 inches of water each time).

In the spring, I leave the water level high (higher than my usual operating level - almost to the coping). It makes removing my very heavy (over 100Lbs) solid cover easier, and gives me plenty of free water to vacuum to waste with.