The protocol I was given is flush every 4 to 6 weeks. I make my appointments for every 4 weeks, but sometimes have to reschedule and I like knowing I've got an extra two weeks to play around with. One time, I accidentally went to 7 weeks, but it flushed fine. The stress isn't worth it though, LOL. I try to go every 4 weeks, just for peace of mind, but I don't beat myself up if I'm a week or two late either.
By the way, sounds like most of you access your own - I'm really interested in doing my own as I've had it for 6 years now, but I'm really freaked out about it. I've de-accessed myself, but that's as far as I've gone.