Residual dishwashing detergent (alkaline, pH 10–12) reacts with animal or vegetable fats to form (saponification). This creates a waxy, grayish-white deposit that is harder than raw grease and more resistant to hot water.
Here is a comprehensive guide to diagnosing, clearing, and preventing a grease-clogged dishwasher drain hose. How to Tell if Grease is the Problem dishwasher drain hose clogged with grease
Unlike fibrous or granular food debris, grease: Residual dishwashing detergent (alkaline