It's not safe to assume all research chemicals will slip by unnoticed. I've seen people claim they tested positive for meth when they had taken 2-FMA, 3-FMA, or 4-FMA (the fluoromethamphetamine research chemicals).If you can guarantee -- and I do mean guarantee, not just "probably" -- that you won't be tested for six days, a lot of stuff will be gone if you hydrate well the days leading up to the test. Marijuana is definitely not safe; it gets stored in your fat cells and slowly leaks out, so you can test positive weeks after you stop. Amphetamines are habit forming, which violates your criteria. The psychedelics would probably be okay -- ecstasy, LSD, that stuff. I don't care for those myself, though, so I don't claim to be an expert on how long they'll show up in drug tests or anything.