This is a really interesting thread for me as my efficiency has been low and I believe the culprit to be using too much sparge water at once. I added just under 5 gallons and ended up with 1.030 - expected was 1.050ish. I am happy to see that the speed of the draining doesn't matter as I don't have a valve installed yet (possibly doing today with toilet braid.
I am using a 5 Gallon cylindrical cooler in a paint straining bag and I am using 10lb grain bills. I still had about 1.5 gallons of dead space so I want to increase my grain bill but I am worried that too much grain may hurt my conversion.
My next batch I am going to do a 2 or 3 step sparge after draining mash tun. Adding 1.83 gallons for each rinse. My question is how long do I let the sparge rest before draining?
Drinking - Craft Brews
Primary - Surly Bender (clone)
Secondary - Zombiedust (clone)