I use my cartos till they're dead, cuz I'm cheap, lol. BUT... I hate the way the flavor deteriorates, the longer you use the carto, the worst your juice tastes. I have been using vodka to clean them, but I think I stumbled on a better method. I have been simply putting 4 drops of vodka in my carto once a day, usually first thing in the morning. Leave it in there, refill, vape. So far I have experienced very little drop off in the flavor or the vapor. I generally top off once every hour or so, but only use the vodka once a day.
Just thought I'd put this up, it might be something that works out for others too...