I've had good success using a kettle and a bucket for BIAB. use the kettle for mashing the grain in the bag, and use a bucket of hot water for sparging. Pull the bag out of the kettle, and put the bag in the fresh hot water. stir it around, pull the bag out, and dump the bucket water into the kettle.
Not sure if the above is actually standard procedure for BIAB, but it's what I did.