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Wow four years on the same filter. That's encouraging. Using hot water is key I'm sure. It would be interesting to know whether you experience an increase in jet pressure with brand new filters i.e. whether there has been a gradual but unnoticeable decline in performance over the four years due to not having changed the filters.I used hot water for the overnight clean. Now I'm going to start using hot water on the spray cleans.Thanks bud!