Generally the most accepted method is triple rinsing. That involves when a container is empty filling the containers about one-fifth full of water, putting the cap on and shaking it vigorously and dumping rinse water back in to the tank and repeating at least twice more. For quick and easy removal of residue, pressure rinsing works well. Removing residue will also be easier if you clean the container as soon as possible. The best time to clean is immediately after they ve been emptied particularly with some products.
Stains are acceptable on containers as long as all residue is removed.
Puncturing containers is also a good idea because it prevents them from being reused. A label does require after containers are properly rinsed they need to punctured and not reused for other uses. I know we commonly see containers being used to haul gas, oil, or water but really pesticide containers should not be reused. By rinsing your containers contents back into the spray tank you can save money and by recycling them you are saving space in landfills. They can be taken to one of the pesticide recycling locations, which will be held in June until sometime in July.