I've seen people on several blogs suggest that fountain pens should be flushed out monthly. That seems a little excessive to me, especially with dye-based inks like Diamine or Waterman, but I'm open to changing my mind if enough people who at least seem to know what they're talking about tell me that I'm wrong. I've gone a couple of months without cleaning some pens with no problems (yet), but I change ink colors often enough that sometimes I'll clean one after a week or two. But I'm talking about staying with the same ink. Thanks.