I'm embarrassed to say how infrequently I clean my lines. I actually haven't done a thorough cleaning since I installed them years ago when I did a major upgrade to my serving setup.
I believe this is one reason why I can go for extended periods though, the line I installed is the bev seal ultra 235 barrier tubing. I also use John Guest fittings for the quick disconnect as well as on the shank, my shank is stainless, and my faucets are stainless Perlick 650ss.
Part of it though, is I have 14 taps, so just the thought of cleaning all of them makes me not want to think about it. haha. My cleaning regimen is time consuming when I do it - I have a manifold that I built with John Guest fittings for the lines that I connect 7 of my lines to at once, then I use my Stainless chugger mini-max pump with a small pot filled with line cleaner (I use 'penetrate'), on top of a camping stove that is heating the solution so that the recirculation temperature is around 130F for 15-20 minutes. This setup takes time, and I also have to do it twice to clean all my taps and lines.