Yes, annual. Why? Because I don’t want to have to rebuild it in an emergency – been there/done that/didn’t like it. So every year I rebuild or service the marine toilet at the beginning of the season, and since I’ve started that, I never have problems with it. This is also the optimal time to service the head, as it has been cleared and pumped clean for winter storage.
I purchased a service kit from Jabsco for my model and year-range. The kit includes three major components, and a bunch of other little parts – all (more or less) critical to the operation of the toilet. There are three main valves that control directional flow of waste: the “joker” valve; the “flapper” at the base of the pump; and the control valves in the top of the pump.