Commando Black Holding Tank Cleaner from Walex Products uses a super-concentrated enzyme formula to fight against tough buildup and unpleasant odors, which is a common problem within a restroom trailer’s black holding tanks. It works by penetrating deep into tank walls to remove waste and paper buildup, cleaning in as little as 12 hours, according to the manufacturer. It is available in bulk tubs of 40 easy-to-use dissolvable packets that are dropped into a tank, which is then filled with water. The recommended usage is two to four times per year, or more or less frequently as needed. 800-338-3155; www.walex.com.