I am a bit curious to know what car has a fuel tank that small. Seems to me it would yield a mighty short fuel range.
Again, from curiosity. Suppose you fill the tank by the usual practice of putting the fuel nozzle into the filler pipe, and fill until the nozzle cuts off. How much more fuel do you get into the tank if you then top it off?
Question 1, a Fiat 126, yes a small range but designed for town use only. Would do over 64 MPG out of town though, so range wasn't too bad. It was basically a Motorbike with 4 wheels!
Question 2, My fuel tank is 35 litres on my current car, but some have reported getting up to 42 litres in. I actually ran dry once, cruised into the gas station with the engine off and only managed to get just over 40 litres in, so different pumps are calibrated differently.
I used to have an '86 Ford F150 pickup. It had, according to the Owner's Manual, two 19 US gallon tanks. Because of issues with the gauge, I usually ran it on the rear tank until empty, then switched tanks. I was never able to get as much as 18 gallons into either tank, even when the tank had been run dry.
I also used to have an '06 Kawasaki KLR650. It officially had a 6.1 US gallon tank. I don't recall what part of it was "reserve". When I ran it into reserve, I could never get more than a gallon less than the official capacity "above reserve" into it.