[userjack6880]

Every two weeks. My tank isn't empty by the end of the two weeks, but it's a good routine. Did that in my last car too. I seriously don't live that far from work, so this is even with about 5 minutes of spirited commuting. :P

I average about 4 tanks a month - 2 for dd and 2 for weekend trips. Sometimes I end up with more full tanks every so often when I take a bazillion trips during a given month or drive aimlessly to destress.