3 days? I make it 2 weeks in a 20 year old car. Sure, if you're doing a lot of driving it won't last 6 months. But for typical everyday use, I bet that's not an exaggeration (certainly not for my use).
I used to go for two weeks between fill-ups in a '78 Buick but that was mostly becuase it had a 24-gallon tank (and I only drove about 20 miles a day).