Never heard of cream of tartar for that purpose.
I know the following due ex cons and parolees that use to work for my dad.
You could just drink copious amounts of water. Drinking large amounts of water will make a urine test be too diluted to work. This will usually get you a retest and a longer time to clean out your system. It requires LARGE amounts of water.
If its a hair test, I suggest a shaved head. :)
If you are taking fat soluble things such as pot, don't lose weight and burn fat because it'll release more in your system.
And of course, stay clean as long as possible before your test.