Originally Posted by librewer
If you do a batch sparge.... everything from the initial mash.
This is not my understanding of batch sparge nor my practice.
When you mash in, you want somewhere between 1.25-2 quarts of mash water per pound of grain. I aim for 1.4qt. In your case, you're looking at ~22 quarts or 5.5 gallons of strike water (initial infusion).
After your mash time expires, you drain the 1st runnings and add the sparge water you've been heating while you wait. Grain absorbs somewhere around .12-.15 gal of water/pound (in your recipe, about 2.4 gallons), so you should get about 3-3.25 gallons first runnings.
If you want to start your boil with 6 gallons, it's simple math from here. 6 gallons pre-boil (goal) - 3.25 1st runnings = 2.75 gallons needed. Since the grain is pretty much full of water, you don't need to worry about absorbtion. Sparge volume is 2.75 gallons... let it sit 10 mins or so while the 1st runnings heat, then drain until you have your 6 gallons pre-boil volume.
The sparge/2nd runnings rinses a lot of sugar that was left behind by the original mash. Should help your efficiency a LOT!