Dishwasher detergent only (i.e., stuff specifically marketed as for going into dishwashing machines)

Absolutely don't put dish soap like Dawn into your dishwasher - it will foam up, shoot out of the dishwasher, and absolutely wreck your dishwasher and surrounding kitchen with foam.

If you're curious what this mishap would look like, check out this image search: https://duckduckgo.com/?q=put+dish+soap+in+dishwasher&t=ffab...