Is it better to fill up at the half way mark or to wait until empty?

[anon9]

Pretty simple. Should you fill up once you hit half a tank and bring yourself back up to full or just wait till empty?

The reason I'm asking is because everyone knows you get better gas mileage from a full tank to half a tank, but I've heard that doing that is bad because you're not cleaning out all the gunk in the bottom of your tank and in the long-term, you will have to get a new gas tank.

I want to know if there's any truth to that.

I had a Honda Accord for about 2 years and did that with no problems, but I just bought an 05 neon and I don't want to risk any long term problems.