Just in case you haven't read about this... for general heads, not
specific to any types.

We race more than cruise and have learned some things the hard way (eg
a clog-up that meant holding-it-in-for-a-day till back on dock, where
the loo door was locked):
1) Use toilet paper that biodegrades easily. I actually tear it up
into pieces beofre use. Otherwise tp stays around or sticks in the
valves.
2) use some lubricant (ours is blue) before flushing
3) only tp, pee, poo, and blue. never ever allow anything else (no
tissues, no baby-wipes, no san.towels, no condoms, no paper towels, no
napkins, no cigarette butts, etc).
4) Make a rule of "pump-out 12 times" (the pumping actually can be
heard) or whatever. This makes sure everything is flushed through, not
accumulating to block up.
5) Have big instructions particularly if you have visitors (people are
too shy to ask, even regular users forget where the seacocks are, which
is pump-water-in, which is pump-sluice-out).

Also see topic 'Heads for small boats' in this group

Last block-up had 3 people dismantling the system (wearing arm-length
gloves) and the rest incl weak-stomach-me gagging above before running
away ashore. Didn't have to replace the whole unit.

Good luck
Solo Thesailor
http://sailingstoriesandtips.blogspot.com Comments and feedback on
stories and the fledgling-new-site most welcome, thank you.