To remove the dirt outside the casserole, you need to prepare the following materials and tools: rag, ash, clear water and basin. The specific cleaning method is as follows:

1. First check the dirt outside the casserole, as shown in the figure below.

2. Take out the rag below for later use.

3. Next, you need to soak the rag in water, as shown in the figure below.

4. Then you can dip some mosquito-repellent incense ash with a soaked rag, as shown below.

5. You can wipe the stains outside the casserole with a rag dipped in mosquito-repellent incense ash. See the figure below for details.

6. Finally, remove the stains on the outside of the casserole, as shown below.