This may be a stupid question but here goes nothing:

I just purchased a brand new 2006 F-150 Lariat Supercrew with the Flex Fuel 5.4L V8. I was told that BP sells ethanol because around here it's hard to find. I was wondering 1st though is it safe to mix gas and ethanol or should I run my tank dry then fill it up with ethanol? How much cheaper is the ethanol? Where can I get ethanol besides BP? I never let my tank get below 1/4 of a tank so I was wondering if I should run it dry then fill it up and if I did would I run into any problems? I've heard nothing but good things about the flex fuel and even had it recommended by one of the Ford dealers on this website but I do not know anyone personally who has used the advantages of the flex fuel. Any feedback would be most appreciated guys. Thanks.