Replace milk filter?

Sequence:  Press the yellow button, then wash your hands. If they are clean, the button will now light up and the filter can be replaced.
Or turn the green button on Duofilter.
Replacing the milk filter with clean hands ensures that the outside of the filter remains very clean. And that’s “the tank milk side!”

It is useful if there is a water hose nearby so that you can easily rinse the edges and thread + knob around the filter canister. When it’s easy, it always happens. And that is necessary because the edges and button must also remain clean.