Hmmm..........a schedule could be:
Once a week.
Once every 3.5 weeks
Every 8th Tuesday
Every 2nd Sunday but only those Sundays that fall on months that have 30 days.
Etc......
Yes so true. Personally, my interval is on Feb 29th... If it needs it or not.
Or - if the performance is noticeably affected - now you will say - "by what standard is the performance measured and what is the trigger point to say it needs cleaning?" Well its a personal choice. If one doesn't notice lack of performance, is happy with the look and feel - well I guess it stays dirty. If you are annal and think the moment you see reclaim the performance is affected or you can't stand the look of some reclaim on your glass you may do it a bit more often.
It would be interesting to blind fold someone who is in the latter camp (more often cleaning) and see if they really could tell any lack of performance or is it really looks... The looks is just an opinion and can not be scientifically measured. I do know the fret or honeycombs require cleaning more often. My belief is the more the perc effect the quicker it gets dirty and the performance is affected the most due to the smaller holes. My recyclers are unaffected by the reclaim with heavy use.
Bottom-line - It must be measured on performance and even then it becomes opinionated...
Perhaps the question could be restated - "do you notice degradation of the pipes performance as it gets dirty?" or "If you notice performance reduction do you clean the pipe?" or "do you clean your pipe even though you don't notice performance lost?" or maybe even "How annal are you?" Simply stating do you let your glass get dirty really is very vague in my opinion so I gave a vague answer, which I thought completely answered the question - sorry I was just playing around