Yes. Here's the pure facts. When taking a test, you have three choices, substitution, dillution, and additives. Additives can be detected but work in some cases, dillution is cheap and works very well when done right, but can also be detected or still fail. Substitution will work 100% of the time as long as you're not monitered and you keep the sample warm (pocket warmer taped around it works well).

Good luck, and check the drug testing section for other useful links and info.