I'm still in the dark as to why it's a "bladder" - and by the way the title of this thread is pretty funny. UTpiper, I hope you've taken care of everything.

I've read the bladder "reduces vaporization." But vaporization where and to what benefit? The fuel vaporizes.. in the tank? Is that bad? Somewhere further down the line? Why would a bladder affect anything after the tank?

I also guessed, but perhaps this isn't true at all, that if the fuel tank is a bladder, then filling it from the pump causes it to stretch a little to hold all the gas, possibly reducing the work needed by the fuel pump at the beginning of the tank because the pressure coming from the bladder (which you really got for free from the pump) is pushing the fuel into the car. Or is that just overestimating the Prius designers?

Prius 2006, bought September 14: