What is the purpose of the dishwasher drain check valve and how can it be checked for proper functioning?

The purpose of the dishwasher drain check valve is to prevent dirty water from flowing back into the dishwasher after it has been drained. To check if the check valve is functioning properly, you can visually inspect it for any signs of damage or blockages, and also test it by running water through the drain to see if it flows in the correct direction without any leaks.