You don't actually need to sparge with BIAB - that's the whole point. I actually picked up a 30l electric boiler with a built in thermostat for a song so I literally do the whole lot in one vessel. I pre boil the water to remove chlorine, add salts and let it cool to about 70C while I grind the grains, sterilise, etc, throw in a steamer basket as a false bottom, then the bag, and add the grains, wrap it in a woolen blanket and set the thermostat for my mash temp, stirring occasionally, then lift the bag and tie it to a door handle over the boiler to drain, bring it back to the boil and when done use a $50 chiller which gets it cool quick enough to achieve cold break - or you can use the no-chill method as mentioned.
I have tried sparging, but it made no detectable difference to my efficiency so have gone back to squeezing, except on dense mashes where stuff like torrified wheat or oats tend to hold the liquid.
