Urine test?

My husband quit smoking marijuana 34 days ago he has to take a pre-employment drug screen this coming Monday!  He bought a home drug test and it had a very faint line but it was negative.  Should we be worried?  I'm not familiar with drugs so I have no idea the time frame to leave your system my husband said he should be fine, but I did some research and I read if you take b-12 vitamins it will hep dye the urine to a yellow color.  I'm freaking out I just want him to pass his drug screen so I'm pretty much open to any and all suggestions! Thanks.