Even if you try to stay clean for drug tests, they can sometimes creep up on you. Even just smoking a joint at a party can show up on a drug test for some days afterwards, so short-notice drug tests can cause problems for a lot of people.
So, is it possible to clean your system in one day? In most cases, no. There are a few cases where this is possible, such as if you've been exposed to second-hand marijuana smoke. For most people, however, it's just not possible to completely detox in such a short time.
Don't give up yet, though. Sure, you can't fully detox, but there are plenty of other ways to get through short-notice drug tests.
Urine drug tests are very common, but they're also fairly easy to beat. The most obvious way to pass one of these is to give them a clean urine sample instead of your own. If you have a good (drug-free) friend that's willing to give you some of their urine, that's great. It's then a matter of working out how to do it without getting caught. Most people work out some way to hide the clean sample under their clothes.
If this seems a bit tricky for you, maybe go for a detox drink instead. Just drink one an hour or so before your test with some water. After peeing a couple of times, you should be ready to provide a clean sample in the normal way. It's much simpler than subbing samples, and there's no way it can be detected.
Saliva tests usually only detect recent use, so you might be okay after a day. If you prefer not to take chances, invest in a detox mouthwash. This is especially useful to have in your locker, because insurance companies sometimes insist on saliva tests whenever there's an accident in the workplace.
You use it pretty much like any other mouthwash. Just swish it round your mouth and spit it out.
Hair Drug Tests
Many fear hair drug tests most of all, and with good reason. The typical hair drug test can detect any drug use in the last 90 days. It's unlikely that a single use will show up, but even this isn't guaranteed. The only good thing is that it takes a few days for drug use to show. This means that if you smoked a join the night before, but you've been otherwise clean for 90 days, you'll pass. Just be sure to wash your hair thoroughly.
For most people, though, this won't be the case. Some people get round hair drug tests by repeatedly bleaching their hair before dyeing it back to its normal color. A simpler solution is just to get a detox shampoo. You use this pretty much like a normal shampoo, but it actually penetrates deep down into the hair shafts to dissolve and wash away drug residues and other toxins.
So, there you go. Even though you can't clean your system in one day, there are plenty of ways to pass a drug test at short notice.