I have gauges on all three kettles (3v2p herms single tier rig) but I only clean any of them when there's enough crud to be visually evident. Using that metric - and allowing for recipe variations that for instance have a lot of oats or wheat - I literally have never cleaned the sight gauge on my hlt, the mlt gauge gets cleaned maybe every 6th batch, and the bk gauge maybe every 3rd batch.
In any case...it's all hot-side stuff so I don't sweat it...
Cheers!