Miles per tank is a bit subjective, we all have different definitions of what constitutes a "tank". For me a "tank" is about 45 liters (right about when the low gas light kicks on). I could easily get another 50-100KM but I don't like to chance it.
Miles per gallon is a much better metric; at least with mpg there's less ambiguity.
Very true. I usually got between 31 and 34 mpg.