I don't sparge with my BIAB. I lose about 2 litres (1/2 gallon) per 5.5 kg (12 lbs) of grist AS (after squeeze
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At the end of the mash I remove my bag and let it drain until its slowly dripping then squeeze the crap out of it. Then my boil takes another 4 L (1 gallon) out. I use the fermenter volume in the recipe builder to calculate the starting volume pre-mash (about 32 L /8.5 gal) which gives me between 24-26.5 L (6.5-7 gal) in the fermenter if I am being generous including trub. I'm usually a little low on my pre-boil gravity but usually over by a few points on my post-boil gravity but I take that into account (a little bit) when I build the recipe.
I used to spend an hour calculating out sparge volumes and final and such. In the end sparge VS no sparge...my no sparge method made no difference in the final beer quality compared to sparging so I cut out the extra time and hassle of the sparge. Saves me time and effort.
EDIT: I mill my grains fairly well and I have been hitting mid-70's % efficiency with no sparge.