I suspect "flow" necessarily demands intense focus, so mundane tasks can't lead to a flow state. Focus is probably the wrong word since that suggests conscious control, whereas most flow seems to relegate consciousness to the role of observer. Two things seem to occur: intensity of subconscious processing, with an absence/minimisation of conscious processing. The task itself is important too, it has to be "important", typically something that requires a lot of practice with the goal of improved performance.