Depends. With MTL/BB/Dot every few weeks (mind you the last time I changed the cotton ink my MTL it’d been a month and was black as fuck). Drippers probably twice per week as it’s dead easy
Incidentally, it hadnt been vaped with as much as i thought would cause THAT much black. It was still vaping fine also, i was looking for a possible reason why vaping was giving me a slight sore throat and some breathing issues for the last week or two.
So far it seems to be the reason. I need to check it more often than once a month apparently. I wish this one were easier to open, i have a whole new appreciation for knurled edges.