Every time. They concentrate the pfas in the water, which bleeds through the cartridge as it sits there between uses, meaning all the diffusion breakthrough has to be flushed every time.

These filters only slow down the contamination relative to water flow rate. Think Of them as big chromatography columns or frontal analysis columns

Wouldn't a carbon filter work better then? If I understand them right it will keep the pfas stuck inside itself and not let it diffuse.

The filters are carbon. Every filter has breakthrough. And the filter components themselves are contaminated prior to construction. This stuff is literally everywhere