In supervised or observed urine tests somebody is physically present to ensure that the sample submitted has not been tampered with or substituted.
In such a situation tampering or adulterating the sample is harder than replacing the sample with synthetic urine, although neither is easy.
We don’t recommend using synthetic urine. You can read about the recommended and legal methods in this article: How to Pass a Drug Test in 24 Hours
Problems With Substitution
Using synthetic urine becomes complicated when there is another person in the restroom.
Concealing the container, ensuring that there is no fumbling while pouring from the container, ensuring the sample is at the right temperature and, for the amateur, there is no noise in opening the container.
Carrying The Synthetic Urine
It is essential that the synthetic urine is properly concealed. One of the most common ways to do so for an observed test is to tape a small plastic bag between the legs so that you can open the bag in a controlled way while simulating urinating.
There are also devices available that can be taped on to the penis or inserted into the vagina containing synthetic urine that simulates urinating.
Some more enterprising, and extremely foolhardy, people try to inject urine into the bladder using a catheter which can cause infections galore.
The main point in transporting synthetic urine into the restroom is that it must be concealed and it must appear to the observer that the sample is being collected through the natural process of urinating.
Practice, Practice, Practice
No matter what method or tool you use to take the synthetic urine to the restroom, you have to practice how the sample will go into the collection cup.
There are horror stories of leaking bags and situations where the sample dropped into the collection cup and beyond because there was no way to control the flow.
Before attempting to substitute synthetic urine in an observed test you have to practice, almost as if preparing for a magic trick!