I recently had a set of 4 year old berkey black filters clog to point back flushing and scrubbing outside did near nothing to improve flow. I took them out and let them dry on counter over night to remind me to replace in am, a friend came over and commented on them and asked if I was gong to potato peeler them…. what is that I asked … well you use blade of potatoes peeler to peel.the filter …. after it works like new and passes red dye test…. make sure you dry filter first or it will take off too.much as media is soft.