I have a half gallon tank, which is located in the trunk...
I dunno how much miles, because it only turns on when Im above 14psi... a lot of that depends on the nozzle you have and the ammount it injects...
For example, mine is maf activated, so it starts at 14psi, think it was around 3.2 or so maf voltage and reaches full injection at the max voltage so that it doesnt reaches full injection... I have the nozzle for 385whp to 435whp...
We lasted about 4 hours or so tunning the car in the street with wideband so that means that its like one and an hour and half on dyna, because we ran into some trouble which we had to sort out, and I had to refill the water/meth tank like 3 times, it consumes pretty fast...