Activated charcoal

Hey, at my job i am subject to random tests, and was wondering about activated charcoal (carbon) used to filter out toxins in water filters and was wondering what if you used it to filter your urine instead. I made a sorta make shift filter to piss through and did one of those home tests which did actually give a negative result, but not sure if it would work with lab testin and stuff. Just wonderin if anyone has heard of using that stuff in this way.

The problem is it would remove the stuff that needs to be there to pass the test too.