I top mine off basically until it's about to spill out and pour into the little drain hole.
Why? So I dont have to get gas as quickly.

Believe it or not, I put in a little under 1 gallon more gasoline if I "top off"

I fill it, it clicks. I wait a second, fill and it stops, wait again, fill, stops, wait agai, fill, stops, I do that until I can literaly hear the gasoline in the tube like righht by the filling spot, UNF.
Sometimes it spills and goes through the drain hole, who cares.

Note: Even doing that I never put in over 11.5 gallons, odd.