Personally I would change the filter twice a year at a minimum. At the beginning of fall (when they change over to winter diesel) and at the beginning of spring ( when they change back to regular diesel). I look at it this way, a little extra maintenance will help the engine run better. This also covers the every 10k drain interval of water from the filter. Since you have to get under there just to drain the filter, why not change it also????
How do you figure that the factory drain can only release water but not fuel? It's a drain. From a single container. There's no separate housing that only holds waterThere is no factory drain on the fuel filter that is only there to drain the water out. As far as filter change interval I'm doing 15k because I started to notice poor perfmance issues around 18K and light smoke at wot. But I also run a B20 blend most of the time.