Allow the roaster oven to cool. Dealing with hot meat drippings is not a good idea. Instead, allow the roaster oven to cool down before you being to clean it. That way you can safely pour out the fat.
Remove any food or meat drippings. If you used the meat rack, remove it and then remove the rest of the food and meat drippings. If you pour all the grease into your sink, it will be impossible to get the roaster oven clean.
Wipe out the insert. In order to remove all the grease you need to wipe the enamel insert out with a paper towel. This will absorb almost all the excess grease that clung to the insert.
Wash everything but the unit. Other than the enamel insert and meat rack, you also need to wash the lid in hot, soapy water. Since you removed almost all the grease in the previous step, this shouldn't take long at all.
Wipe down the outside of the unit. In order to clean any spills from the outside of the unit, you just need to wipe it down with a damp cloth.