The Fishmate Pressurised Filters feature the 'Powerclenz' cleaning mechanism (except the 5000 model).
Just turn the dial from 'normal' to 'clean' and the water flow changes direction, back-flushing the filter, and the foam layers are sqaushed which removes the dirt and sludge.
The dirty water is then pushed out of a second outlet, down the drain or into your flowerbeds.
Bradshaws Direct (UK) - suppliers of pond liners (pvc and butyl liners), underlay, pond pumps, filters, pond vacuums, fish food, water features and many other water garden accessories.