*chant* check the search button...
I KNOW I have scene info out there about it. Whether it was on bluelight, or erowind or lycaem or what... its there (but I can't remember where!) http://google.com and http://raging.altavista.com are also your friends.
There could be a few threads around on this topic already, but off the top of my head, there are a couple of ways to reduce your concentration level outcome - there are probably a lot of ways.
Firstly drinking a lot of water prior will help to dilute any chemicals in your system. Since you say "random urine tests" I'll assume completely unscheduled tests, so this may not be viable.
Secondly, people often mention that taking your sample from the middle of the 'stream', ie when the flow is fastest (not the beginning or end where you're slowing down), is another way to have minimal concentration results for a given total body content.
Someone who's gone through this will probably be able to help - might be helpful too if you mention which drug residue you're worried about... THC can stay in your system for a long time, whilst amphetamines can be cleared to a low level in under 96 hours ideally.
BigTrancer