Hi. Yes, the glass stem/pipe. How often would you say you clean it? Every 3-4 months?
As others have mentioned , there are a few variables .
Like how often you use it , Daily or only on weekends ...
What temp you use it . If you're strictly a low temp sipper
Higher temps produces resins faster , I find . Dry herbs or damp .
What you use , flowers , hash , concentrates has a factor in this .
Do you use a screen to keep the debris from getting sucked up .
Even your inhales , hard or slow . Like when you use a bubbler .
The bubbler is my main cause for cleaning stems/gongs .
But it's all up to you , what you deem is dirty or not ...