I have had friends use Golden Seal and it worked and I had a friend who drank a shit load of vinegar. I know it taste bad but there is something in vinegar and it worked for him. Also there is a thing called Urine Luck. Had a friend try that before and it worked for them too.
But be careful when your urine is too clean they get suspicious too, but like someone said that is better than a dirty test.
Good Luck!
