Rookie question. I know it sounds like a simple problem, bit I can't figure out an easy way to get out the unused granular fert left over in the machine. I have been using a push spreader for a couple of years, I would just spin it upside down and pour the leftover back in the bag. But obviously that won't work with a riding spreader. So what do I do if I need to switch product between customers, or at the end of the day when I want to clean up?