If you're putting your car into storage, you know you have a lot of preparation to do so that the car stays in great shape. Storing a car for a short time usually doesn't require too much work, but storing for a long time, or storing during adverse weather (such as winter in the northeast), requires a lot more protection. Your fuel tank, especially, needs to be cared for properly. Depending on the length of time you'll be storing the car and the weather during that time, you may have to have a full tank -- or a fully drained tank.
Why You Might Want to Drain the Tank
Car gasoline isn't the most stable material. It does deteriorate, and it can leave deposits called varnish on the inside of your tank. The fuel can oxidize and become rather useless. There are additional fuel stabilizers you can add to the tank to keep the gas good to use. But modern fuel plus these stabilizers still lasts only so long -- about a year in general.
If you have to store the car for more than that, and no one will be able to go start the car for you when it's in storage, then draining the tank is the best thing to do. Leaving gas in the tank when the gas has deteriorated will just lead to the aforementioned varnish. You may still be able to drive the car with the old fuel after taking it out of storage if you add some new fuel, but deteriorated gas still isn't good for your tank in general.
To drain the tank, you can either literally drain the gas out, or you can let the engine run until the car runs out of gas.
Why You Might Want to Fill the Tank
However, if you're not storing the car for that long, then you do want to leave the tank completely full with a stabilizer added. Space in the gas tank is space in which condensation can form, and this is a particular problem in colder weather. The condensation can drip to the bottom of the tank, eventually settling there and freezing if the temperatures drop below the freezing mark.
Fill up your tank completely at a station close to the storage facility. Add the stabilizer and let the engine run for a few minutes to allow the fuel and stabilizer to mix throughout the tank and system.
There's one other time when you'll have to drain the fuel out of your fuel tank -- if you're storing the car in a facility that doesn't allow the storage of flammable products like fuel. If you're storing the car over the winter or for a short amount of time, ensure you find a storage facility that allows you to store the car with a full tank. If you have further questions about storing your car, contact the car storage facilities in your area to find out what their suggestions and requirements are like.