Forget the drop-in additives. They will not work on instant-type tests because they take approximately 90 min to destroy the drug metabolites in the urine sample. In addition, labs have been detecting additives on a more frequent basis than ever before. They are detected when the sample gets flagged for excessive nitrites, high chromates, and/or an abnormal pH.

Using synthetic or a clean persons sample as a substitute would be a better bet. Its easier to pour in a sub than fumbling around with additive vials in the bathroom stall.