Leave it up to Mercury to make it difficult haha. But their filter is more than enough, unless you know water has gotten into the tank.

I did say he "could" put a fuel/water separator on ... not that he "should" !!

Seems that some Merc engines already have a "filter" & don't recommend adding any more "in-line" filters, for the very reasons that Steve has stated. Good catch, Steve !!
I didn't mean to imply you were trying to give him bad advice. If it weren't for the optimax series, we could just about all run them