the danger with storing diesel over a long period of time is ..... water!

With day/night temp variations, water condenses and sediments at the bottom of your tank. So , if your intake is too low, you will first pump some water out of your tank. therefore, it is recommended to either rotate regularly, or fill up the tank so that as little air as possible remains in the tank.

Note: when wintering your equipment, you should do the same: either empty the tank and keep it vented so it can dry up or fill it up.

I have a friend that had a Steiger with a 4XX gal (1500 Litre) tank. He used to fill it up. Tractor stayed unused for over 2 years in the shed, then found a buyer, when he started it, it kicked on like it had run the day before....