A saliva drug test is a newer method of screening for drugs and can be quite a bit easier to pass than urine or blood tests. The main reason is that it's a very quick and non-invasive procedure. The sample is collected using a sterile absorbent pad that the person being tested swabs inside their mouth, generally against their inner cheek or under their tongue. Depending on the test kit used, the sample can be instantly analyzed on-site or sent to a lab for further analysis.
The detection window for THC, the main component of marijuana, is about 24-48 hours with a saliva test. That's a far shorter window than with urine or blood tests, which can detect substances for up to four days after use. The tests are also highly dependable, with dedicated personnel conducting them and no easy way to cheat the system by dilution or adulteration.
Oral saliva tests work by collecting metabolites, which are the residues of drug consumption that leave evidence in the body. These metabolites move as waste to the saliva as they are broken down by your body's liver, kidneys, or other organs. Rinsing your mouth, rinsing with mouthwash, chewing gum, or taking certain herbs will not remove these metabolites from your saliva before a test.
The only way to make sure you can pass a saliva test is to stay away from all drugs. If you need to take a saliva drug test for work or other reasons, it's not difficult to do, but you should start preparing immediately to avoid any pitfalls.