The easiest, cleanest way to clean a grinder is to run Grindz through it every couple of months. The following is from our partners at Urnex:
Before using Grindz, make sure to empty your hopper of any old coffee and adjust your grind a 3-4 steps coarser.
Add 1 packet (35 g) of grinder cleaner tablets into empty grinder.
Grind the whole package through your grinder and discard.
Add 40grams or 4-5 tablespoons of old coffee to your hopper.
Grind the coffee to help push through any Grindz left in the burrs and discard.