Check out the Drug Testing forum for a better response, but, in a nutshell:

Drink tons of water, cranberry juice as well, and exercise and start sweating. THC gets stored in fat cells, so when you work out and start sweating, in combo. with peeing from the water, it drains your system of THC.

And a drug test at Wal-Mart? Now THAT sucks balls. Don't they get enough satisfation screwing their employess like cheap hookers.