I dated a chick a few years back who worked in a lab as a tech. She told me "the solution to pollution is dilution". Her advise was drink lots of water until you have to piss,once you go the first time pop a multivitimin , piss again then give you're sample on at least the third. If you have a few hours time before making the LOOOONG walk to the bathroom with the sample collector this will work. I have done it. I also habitually drink green tea and cranberry juce when I feel the day may come and I am not prepaired. From her info, the first piss or two of the day are very rich and telling samples.