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.

Gross. Various reasons can cause a dishwasher to back up into the sink, and often, you might not be sure where to start. A garbage disposal backing up and a clogged air gap can be culprits ...