As long as u were completely clean before this, two hits and your clean in 24hrs at the most. I have taken thousands of U.A.'s. If you are really that worried buy a home test kit and test yourself before you go. Pending on how many drugs you want to test for, they are $20 -60 That is is for a reliable one, and they are found at Walgreens.....
I have failed tests with the best of the best detox solutions from pills, to drinks. I havn't tried the bleach thing indoseedman speaks of, but if you ask me it sounds like a good way to end up in the Hospital, if not the test will probably come up tampered with if it goes to a lab, if it is a litmus test it may work. I would bypass putting the bleach thru my system and add a diluted drop to my piss by using a Visine bottle or something. The best thing is WATER the day of the test. Drinking water for days before will just make you piss alot. Water doesn't remove THC it dilutes your piss so you piss water. You can take B12 in double strength a few hours before the test to turn your watered down piss yellow. If your test is getting examined at a lab it will come back as diluted, if it is a litmus test you will pass but they may look at you funny if it is clear. Wow I got carried away there!