In close to 25 years of ownership, and over 21 years selling these things, I have only flushed once - and that was the time I was given a sample kit of EcoOne to try out. The flush was part of the normal start up for that system.
Also - I have begun to sell a flush product for my long-term Baqua users. It seems to be a must due to the gunk that Baqua tends to build up everywhere in a system.
Other than that - no.
bump - anyone else want to chime in on this???