Cleaning involves:

Assessment: Testing the oil to determine contamination levels.
Filtration: Passing the oil through filters to remove particles.
Water Removal: Using vacuum dehydration or coalescing filters to eliminate moisture.
Adsorption Treatment: Removing dissolved contaminants and oxidation products.
Re-additization (if necessary): Restoring essential additives to the oil.
This process restores the oil’s properties, making it suitable for continued use.