Is it better to top up fuel at half a tank or to refuel when almost on reserve?

Is it better in the long run to top up fuel at half tank on a regular basis or to refuel when almost on reserve?

Can I syphon the diesel out of my car?

Could you please advise me how to get diesel out of the tank of my car that is possibly going to be written off? There is £40 worth in and we've tried to syphon it out but there is a something stopping...

My car has been sat for six years with some diesel in the tank - should I drain it before starting it?

I have had a 2003 Mercedes-Benz E320 CDI sitting on the drive for the last six years with some diesel fuel in the tank. Now I am about to restart using the car again, do I have to drain out the old fuel...