It's not a terrible idea to clean out your truck's intercooler before installing the can. That way you're starting from a clean slate, and you'll be better able to gauge the effectiveness of the can. As far as draining, how fast the can fills up is almost entirely dependent on climate, and you may need to empty it once every three days if you're in a cooler weather. However, we here in Phoenix only have to empty our can out once or twice a month.