How often do you change water separator filter?

[T680]

Jt84 are u using fuel additive right???? Seems to me that by using power service gray bottle the water separator stays low longer than wo it....
I change mine usually between 30-40 k miles and the engine fuel filter but not before the water sep gets filled with fuel....I drop fuel twice in these miles from it to clean the contamination .....
Since the water sep is 10 micro , the engine filter is 5 and I use most of the time the ff5686 that is longer than ff 5776((factory original)) for now 309k miles its fine..