Final answer:
The third step in washing dishes in a three-vat sink involves thoroughly rinsing the dishes to remove soap residue and any remaining debris.
Step-by-step explanation:
The third step in washing dishes in a three-vat sink is to rinse them thoroughly. This process involves removing any remaining detergent and debris from the dishes. To do this effectively, the water should be clean and flow over the dishes, from the top downwards, so that it can carry away any soap residue that could potentially affect the taste of food. This step is critical for ensuring that dishes are ready for safe use without any contamination left from either the cleaning agents or the food particles that were initially present.