I change them in both boats (one IO, and one outboard) once a year and always take a spare along if we travel and take boats in case I get a batch of crap gas. Typically they are clean when I dump old ones into glass jar.

I Change them every time I change the oil. I also Do an extra one in the spring after I run the first tank of fuel through it. Sure it is overkill, but it is cheap insurance of not having a fuel problem.