I recently made one out of an empty No-Doz bottle with a hole cut in the back and an emptied-out pen tube stuck into the hole. I Used a tinfoil bowl, and the little thing actually works quite well. No too fancy, but it works.
I don't think they clean out your system, I think they just block the toxins from being excreted for a few hours. I think you should have taken that drink a few hours before your test, but I could be wrong.