That is unfortunate that there are no re-fill boxes available. (what are you supposed to do , just keep re-purchasing the trick , even though all you need are the replacement boxes ?) Traditionally you end this trick by casually ripping open the cardboard detergent box to show it truly empty . It's showy and is a natural applause cue when you do that. What you could do is use a real detergent box like 'Arm & Hammer Laundry Booster' or '20 Mule Team All Natural Borax Laundry Detergent' (two of the remaining brands that still market in traditional style detergent boxes) and make the box re-usable with a few careful cuts with an Exacto knife and attaching small velcro tabs, so you can flip open the box to show it empty (instead of actually ripping it open). This way the box can be re-used for multiple performances.
