Soak this dirty little guy in coffee detergent with hot water. Then clean it again with a wire brush if needed.

Make sure to clean out all the water channels on the back side of the diffuser.

On Version 3 you will need to remove the brass disc. Just lift it out. If it is stuck you can use a channel lock pliers to get it loose. Be gentle! Careful not to damage the brass. You cannot remove the brass disk on Version 1 & 2

This is the brass disc after it is been removed. Soak it in coffee cleaner with hot water for about 10 minutes. Then, scrub both sides with a steel brush. Get leftover coffee residue off disc.