Pseudo sparge BIAB can be done in a smaller pot, but you will need a second pot to heat sparge water. I use a 7.5 gallon turkey fryer for the mash pot, and a 5 gallon (formerly used for extract )pot to heat sparge water. I mash at more traditional AG thicknesses of about 1.25-1.5 qt/lb of grain. then I pull the bag & drain through a colander. after draining, I pour 1/2 the sparge water through the grain bag, and then tea bag the bag into the sparge pot. Fire up the boil kettle while finishing the sparge & re-draining the bag. add remaining sparge water and boil.
5 gallon paint strainer bags work great. You need a bag big enough to hold the grain, not the full vloume of the pot. clip the bag to the pot edges with binder clips.