One arrow you might want to add to your quiver for head meintenance/longevity that I have found very helpful is to keep a squeeze bottle (used liquid soap bottle or whatever) with a mix of SaltAway and water in the heads. We have and when anyone uses the head, once they've pumped the bowl empty and flushed the system (at least 5 added pump strokes please) we ask them to put a good squirt of the SaltAway mix in the bowl and give the pump a few more strokes. Getting this material into the waste lines prevents the built-up of salt and calcium carbonate in the lines and seems to help preserve the flapper valve and joker valve and our heads remain clean and functional. I do a maintenance call on the units (we have two) annually but can easily get two or three years on a set a valves (more if I wanted to push the issue). While SaltAway is not inexpensive, one needs only 1+/- oz in a large (34 oz) squeeze bottle so it is a cost effective way to help maintain the head equipment.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."