The Gen 2 has a rubber bladder inside the fuel tank so we're guessing as the car ages, the rubber bladder becomes less flexible so it doesn't quite fill up the volume of the fuel tank like it did when the car was new.
In my experience the best way to fully fill up a rubber bladder lined gas tank is to drive it down a highway in 100' weather for many hours. It holds the most when you refill it after that. The opposite is true in freezing weather. Folks in wintertime US midwest on PriusChat have actually reported rubber bladder puke, as in gasoline coming out of the fill pipe and soaking them... Rubber bladder was a great idea to reduce pollution by eliminating the evacuating of polluted air as tank fills, but thankfully, the newer Prius have better ways these days and rubber bladder is no longer being used, or at least that's what I've been told.
Not that I know of, short of replacing the fuel tank with a new one. It was one of things that was annoying on our 2005 Prius; it held less fuel by the end of its life (11.5 years). To be fair, it didn't hold the full 45 litres when it was new anyway. I think the most was 38 litres on my record tank of 902km but that was a one-off. Most of the "full" tanks were 32 litres. By the time we traded it in, it was down to about 27 litres on the low fuel light.
The EU and other regions don't have the bladder version so those parts, used or otherwise, are indeed available... But most of all don't forget the irony of people complaining about fuel tank capacity for a car that's barely 10 gallons, yet having no complaint about range on a full tank? Compare that to all the other vehicles Prius share the road with who get the same range but have to have 20, 30 or even 40 gallon fuel tanks to spend their money on. I mean who's the smart one and who's the fool? I'll take any and all complaints of a gas tank being too small if there's no complaint about range... Not even Tesla can beat that kinda range with no one having to complain.
maybe a custom tank swap from a euro model or gen 3. sounds complicated though. unless it won't take any gas, i'd just live with it. and i did with 2004 and 2008.
You'd have to find a way to ensure the tank sensors for a bladder system don't get triggered by a bladder free system. Maybe fooling the ECU, or maybe Toyota TechStream diagnostic software has a way to do it?
Maybe if you sat in an armless chair and exercised your inner electrical engineering geek more often?
Today was a very good example of your experience for me. I normally have the car garaged and fill it up about 6 or 7 am before it gets too hot. My last three tanks were 42.5, 46.7 and 47.8 mpg. Today we drove the car around town all day in the 100* heat and decided to top it off at 5 pm before leaving on our trip after midnight tonight. For some reason the pump I regularly use was operating slowly. A very pliable, warm bladder combined with the slower than normal fill rate resulted in an mpg of only 33.5. No worries because I know from experience it will all even out on the road to Colorado tomorrow but if I were new to this car I'd be panic stricken.
Having just returned from the trip, I wanted to report that the mpg rebounded exactly as predicted and then some. Taking the I-15 and the I-70 over the Rockies the car performed like a champ. Tanks on the trip were 50.9, 45.1, 54.3, 49.3, 37.4 and 48.9. The low tank was a result of my wife deciding to use the cruise control all the way through Utah on I-70 during the return trip. I prefer to stay to the right and drive by feel while listening to the ICE, backing off a bit rather than winding it out on the long and steeper climbs. The car handled the high speeds very well the rest of the time. Average round trip was 45.5 mpg. Just another example of not allowing any single tank result to upset you. It definitely takes multiple tanks.
It is a way of Gen 2 in North America. Live with it as fixing it is way too costly and unnecessary. The range of the car is so great that it really is not an issue. I can fill 10+ gallons in the summer and barely 8 in the winter (sometimes more), but my range is never less than 300+ miles on the tank, which is fine. In the summer my range is more like 450+ miles per tank. It's definitely weird and the first car ever to do that, but once you get used to it, it's just another one of these quirks. Enjoy the rest of the car!
