A.R.S. § 44-1244

It is unlawful for any person to place, store or keep, or cause or permit to be placed, stored or kept, for the purpose of sale any petroleum product in any storage tank underground or otherwise, or container or receptacle which contains or has previously contained a different product, or the product of a different manufacturer, refiner, producer, or marketer unless and until such tank, container or receptacle has first been emptied and relabeled in accordance with this chapter.