If i drink a gallon of water how many hours before i take my drug screen should i take a b 100 complex vitamin pill to put yellow bk in my urine n will the riboflavin cause me to get a false positive drug screen for thc?

THC will show five to seven days after the last consumption for moderate users, while this becomes ten to fifteen days for daily users. Meanwhile, heavy, long-term users can fail a urine test a month after consuming marijuana. ref: https://thebeachcomberrehabilitation.com/

Diluting your urine by drinking water will not be overcome by making your urine yellow with riboflavin. The lab should measure urine creatinine and will know that urine is too dilute for a valid test.