Here are some basic guidelines to follow to purge your Brite tank (or similar vessel) with CO2 before you fill it. While there is not a specific way to do it, here’s a couple different methods that people use to accomplish this. First, your Brite Tank should already be cleaned and sanitized at this point, if you haven’t yet done this, please refer to the quick reference guide. Also, just about any book on brewing will have a section that covers proper cleaning/sanitation techniques (just be careful to follow our warnings about bleach and oxalic acid based cleaners).
In the first method you’ll connect your CO2 line to the carbonation stone port. Close all other valves but leave the lid open just slightly to allow gas to escape. Turn on your regulator and simply vent some CO2 into your tank for about a minute (just a couple PSI for about a minute will do, you don’t need to go “full blast”). The theory here is that the CO2 will displace the O2 and then you’ll effectively have a CO2 blanket as you fill (physics is on your side here).
Another similar method is to fill the tank entirely with water then close it up and use a couple psi of CO2 to evacuate the water so that the entire volume is theoretically filled with CO2. You’ll then crack the lid and begin filling the Brite Tank with beer from the bottom. The theory on the second method is that you can get more oxygen displaced and replaced with CO2. Although the first method has worked well in my experience.