Remove the piston gasket and clean any coffee from the channel it sits in.

The top strainer gets a bath in some degreasant. A tooth-brush can penetrate every pore of the strainer. Sometimes can help a tooth-pick. In some cases, a needle will help you too. Rinse with water.

Take a look at the strainer, hold it towards the window or some strong light. you should be able to look through every hole. Well done.