If using over an extended period of time, it build's up in the cerebral spinal fluid - lymph and other non circulating bodily fluids.
So staying out of trouble, consuming lots of cranberry juice increases the acidity of the urine and shifts the partition of coefficient in the nephrone of the kidney in favor of excreting the toxin more rapidly.
A last ditch method of avoiding detection is to get some powdered bleach, on the finger tip, finger nail and rinse it off in the urine sample. bleach attacks the toxin by oxidation, converting it to a harmless set of fragments.
Remember to drink lots of water lots. And give the smallest urine sample possible and a lot of bleach, this also works better with more easily oxidized substances such as thc.