The lower manual can be used either for playing walking bass, or comping chords. For the former, 808000000 works really well; add more of the 2nd drawbar to get a heavier, more ‘growly’ tone. This setting is not ideal for playing chords on the lower manual, since this makes the sound often too muddy. 008800000 seems to work better for chords down below, or you can just play them higher up the keyboard if you want to switch between walking and comping.
It is often is suggested to turn off V/C when using a walking bass – I think it can work either way, depending on the mood of the song. You can also turn off the bottom rotor to get that ‘Memphis’ sound, which also works well with walking bass lines.