Step 4. – Flattening

Still with 20 mm sealing brushes on, set the router bit 3 mm (☝only if your tools allow it!!!) deeper and plane the highest area of the slab.
Put on 30 mm sealing brushes and keep planing with a depth of cut 2mm.
Put on 40mm sealing brushes as soon as the gap appears between the sealing brushes and the wood, and keep planing with a depth of cut 2mm.
Check the bucket, and empty it if it is full.