Take a Bb minor pentatonic scale
[Bb Db Eb F Ab]
Now play these over a progression in the key of Db major. You will find that these notes work well over the chords I IV V ii and vi. Probably iii and vii as well, though I haven't explored these as much. There is some tension in the tritone sub.
If you play an F minor pentatonic you also get a good set of notes to play in this key.