That strange round silver R2-D2-looking thing, to the side of the kitchen faucet, is the dishwasher’s air gap. When it gets full of gunk from debris left on dishes, the dishwasher can’t drain.

The connection should be placed above the P-trap on the drain line to prevent sewer gases from entering the dishwasher. • Air gap to disposal: This configuration has a drain hose that runs to ...