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 air gap cylinder is another essential component of your dishwasher. Its primary function ... sits right on top of your sink next to the faucet. Inside this cylindrical cap is the drain hose.