Well we have gone and done it! After much research
and concern, we have purchased a "Natures Head", Dry Composting head
The unit was quick and easy to fit ( so easy I was convinced that I had missed a bit out), just assemble it, bolt it down, put the peat in, connect up the air pipe and that was it.
It does not smell, it is almost silent in use, Nita (My Wife) approves of it.
It is possible that the urine tank could be bigger, only holds 2.2 gallons so needs to be emptied each morning, but this only takes a few seconds.
No discharge overboard
, no fouling of the environment
, no holding tank
with gallons of effluent swilling around inside our home. No pipes to clog with calcium, and no sea cock to leak.
That is it, we are convinced!