I generally fly sparge. I have a Stout mash tun with their sparge arm. I have a pretty good history on my system's volumes - what the mash tun holds, how much liquid is retained my my grains, etc., and sparge enough water to produce the pre-boil volume I need for any particular batch. I drain virtually all of the available wort (unless I over shoot my sparge, then I just leave that behind). I use a pump to transfer the wort to the boil kettle, so it is a little bit of a game to balance the wort coming out of the mash tun with the sparge water going in to keep the level right in the tun. And then another game to move the rest of the wort out without collapsing the grain bed. But for me, the process is part of the fun in brewing.