I know that he's getting a hair test and so this is meaningless butttttt I know a thing or two about piss tests. I've taken well over 1000 in my life and that's no bullshit. I was in the military and I've been on methadone for 4 years, which means 2 tests a week until you start getting takehomes, then restarting that whole process every time you fuck up (failed test, missed appointment, forgot to bring your bottles in, someone tattled and said you've been a bad boy etc) and that's with a dude standing beside you watching you piss in the cup.
Almost every product that claims to be a "detox" is a scam. Ever notice how they all tell you to drink a shitload of water with the product? That's what passes the test for you - dilution and nothing else. Weed is weird and even a heavy daily smoker can pass a test with marginal dilution if you don't have a lot of body fat. Always piss as many times as you can before you go in. B vitamins will help with the color and a good multivitamin and creatine helps to prevent being flagged for dilution. Niacin doesn't do anything (other than being a b vitamin) except make you red and itchy. Cranberry juice/vinegar/yak piss etc is no better than water, so save your money. If its just weed your best bet is dilution and not being fat. You can try using bleach or another powerful oxidizer but some tests detect that.
There's a ton of wives tales and snake oil in the drug testing world because, as I mentioned earlier, there's a lot of variability in terms of results and testing methods. Add to that the fact that most dip-stick tests (which is what almost all employers are going to use since it's cheap) are notoriously inaccurate, and you have guys who eat their own jizz then pass a test and swear it works and it spreads like wildfire on the internet. I've passed piss tests 2 hours after shooting up and I've failed ones after 10 days of abstinence. I failed a test after eating 2 pepperidge farms everything bagels, so don't believe anything anyone says about how you need to eat a bunch of poppy seeds to fail. So far I've tested positive for 4 drugs I've never done in my life. It's a super fucked up, insanely lucrative market with very little regard for standards or science unless it suits their agenda.
Sorry for the rant, but yeah... if its a hair test you're fucked. If you just smoke bud then drink a few gallons of water, piss a few times before you go, and you should be set.