Concur with all the others. I've used Roundup months after I mixed it and it still killed the weeds. Use it around my trees with no problems too. I've also alternated RoundUp and insecticide in my Fimco 15gal unit after a thorough rinse with water. Noticed the other day at Tractor Supply they have a "spray tank neutralizer/wash". I didn't look at it in detail but maybe it's just a detergent that helps ensure a good rinse....