This recipe is made from less caustic ingredients than many of the dishwasher detergents you'll find on the supermarket shelf.
Add optional essential oil.
Mix until well-combined. The mixture should be slightly damp. If it still needs more moisture, or if you're not using essential oil, use a spray bottle to spritz on a little at a time. Don't add too much water!
Press firmly into ice cube tray or mold. You can do a test with just one tablet to make sure it holds its shape before adding more water.
Note: These images show homemade dishwasher soap tablets made with a bit of food coloring for photography purposes.