Whether or not a slow cooker can be placed in a dishwasher depends on the specific model and the manufacturer's guidelines. It's essential to refer to the instruction manual that comes with your slow cooker to determine if it is dishwasher-safe.
Many modern slow cookers have removable stoneware inserts and lids that are dishwasher-safe, but the electrical base or the entire unit with electrical components is not. The electrical base should never be submerged in water or put in the dishwasher, as it can damage the electronics and pose safety risks.
To clean a dishwasher-safe slow cooker, you can remove the stoneware insert and lid and place them in the dishwasher for easy cleaning. However, if your slow cooker's parts are not labeled as dishwasher-safe in the manual, it's best to wash them by hand using warm, soapy water to avoid damaging the non-dishwasher-safe components.