Stanky, I'm glad to hear that you can water load like crazy and still not get a dilute results. I wish it were the same for the rest of us, but that's just not the case. Drinking a large amount of water just before a test is the oldest trick in the book and labs try to counter that trick by testing the urines creatinine levels and its specific gravity. If the creatine level is below 20mg/dL and the specific gravity is less than 1.003, the sample is tagged dilute. The waterloading link that is no longer working in my dilution guidelines showed creatinine levels when folks diluted. A few lucky folks never got a dilute result while others easily got dilute results.
The vitamin thing is also a great trick to add some color back into the urine.
:!)
N2

PS. dilution is not 100% effective. If you're initial levels are more than 10X the test cutoff or higher, dilution will likely not work.