You arrive at the fuel truck with an empty tank and order up your preferred flavor. Rick Gold (or his helper) looks to see that the tank really is empty, then puts in how much of what you want. He then takes a piece of duct tape (or something) and tapes the cap closed, paints a few dots of color-coded nail polish on the tape/tank boundary, and date-and-initials the tape.
If you qualify for a record the impound folks will probably come take a sample from your tank even though they've also looked at the seal to see that it's still untouched. They do reserve the right to sample your fuel before you get to impound -- for instance, at the end of the course while you're waiting to tow back to impound.
Assuming you get back to impound after your return run the next time out you'll have another sample taken, and both can or will be checked for forbidden substances. if they're satisfied that you're running "legal" fuel you have passed that portion of the record certification process.
By the way, should you need more fuel (to make your return run, or whatever) after you've had the tank sealed, you can get it -- but you need to have the sealed tank opened in the presence of an inspector, filled, and re-sealed.
If you run a gas class and really want to do your tune-up and your dyno-ing at home -- you can purchase ERC and use it for these purposes, and then buy more of the same stuff at the track. Or -- if you really really want to use your own favorite bug juice -- run in fuel class.
I wouldn't be surprised if you could use a non-event fuel in gas class as long as it would test legal, but a minor -- but important -- reason for using event fuel is to support ERC for making the trek out to the Salt each year to make sure we have good fuel available. Thank Rick as you go to the truck, hey?