If you are like me and have other diesel powered equipment that gets used more often than your generator it is a good idea to rotate the fuel. I have only topped up my generator after each monthly load test for the 6 months I've owned it. I had to refill my storage drums a couple of weeks ago since I used all the stored fuel in my tractors. Today I pumped all the fuel from the generator into my backhoe. I will use that much in a few days digging stumps in that machine. I refilled the generator from the treated fuel in the storage drum. I think a 6 month interval on this should make sure I always have fairly fresh diesel in the generator as well as the external supply drums. It looks like I am going through about a 100 gallons every 3 to 4 months running my two tracltors.