Coffee filters can be washed in a variety of ways, but it is not recommended to use detergents or dishwashers to clean coffee filters because these substances may damage the filter surface and reduce its effectiveness.

One method is to use a damp cloth to wipe the filter surface clean. Use a mild detergent such as dishwashing liquid or mild soap to remove any remaining coffee grounds. Then, rinse the filter with clean water to remove any remaining detergent residue.

Another method is to use an ultrasonic cleaner. Insert the filter into the ultrasonic cleaner and turn on the machine. This method is effective, but it may damage the filter surface.

Finally, if none of the above methods work, you can try to remove the filter by hand. Remove the filter from the machine, place it in a clean, damp cloth, and wipe it with clean water. However, do not use anything strong to remove the filter, as this may damage the machine or the filter surface.