Old gas in tank, what to do?

Please don't over-think this. Just drive the car. The Gen 2 has a very well sealed fuel tank.
Even the Z71 4WD pickup my wife inherited from her father in Ohio started right up (with a new 12v battery) after sitting for >3 years and it had small holes rusted into the top half of the fuel tank. Don't over complicate it. In the real world, one year is absolutely no problem. Heck, there's probably many Primes out there that have a single tank of gas last over a year when most trips are performed on just the battery.

 

I left my toyota truck over three years with the same gas. I started it, took it to be smogged with my legal operating permit from the dmv to start the registration again from being on non op. It passed easily and never had an issue, on the old gas. I was researching how to empty the tank, bought a new fuel filter, but then said going to try the easy way. So saved me a lot of work. It sat outside.
I attribute it possibly to the use of e10. Straight gas there may have been a water layer sucked into the fuel pump, an electric type in the tank.

 

The Prius just means we can ride more that's it We still go through fuel like water always halves since I was a kid still do got scooters and motorcycles and powersports stuff couple zero turns you know a tractor and so on just getting a vehicle that gets 40 plus miles to the gallon means we can go farther whatever so far in my lifetime I have never seen a tank of gas sitting in a vehicle longer than about 4 days I think that's right yeah about 4 days that's it and I run it the tank that is almost to empty plus a few drops running out in a generation too is of no consequence You just need a milk jug or something full of gas to dump in the tank give it time to run down the filler neck and be in the tank actually and go up and push the button and don't do anything just sit there for about 20 seconds and then pull the car to drive engine will start right up It has the beauty of an electric fuel pump that's one of the reasons we have it I've never had to prime an electric fuel pump vehicle ever It may take some vehicles a few seconds to a minute or two possibly for everything to equalize get situated get pumped to where it needs to be but it's going to happen without your assistance for the most part.