As I said, if you have a permanently installed MSD (e.g., factory installed) you, by law have to have a holding tank in USA waters. See: The West Advisor: Heads Holding Tanks
and lots of other references
. The CF threads about installing composting toilets are pretty much directed at removing the potential hassles of potty police, etc.
That holding tank capacity can be one pint to many gallons, but needs to be there along with the other required valves, etc.
Add in the USA situation with "No-discharge Zones" and you can see that anything less than a reasonably sized tank will quickly become full and then you are "S... Out of Luck" being able to use your on board MSD facilities.
Then add in that in more and more places the LEO's are dropping dye tablets into your MSD system so you cannot "cheat" and pump overboard
when nobody is watching - supposedly.
Add in the average intelligence level of the "potty police" and you can anticipate a high level of hassles if the holding tanks do not exist anymore.
You will be severely restricting your cruising areas if you remove your holding tanks to 3rd World countries without "eco-conscious" zealots.
Again, no problemo if you cruise
away from 1st World places - but over the years I have watched cruisers "modify" their systems and then when it comes time to sell the boat they end up paying significant money
putting all that stuff back into the boat and getting it working again.
Is it really worth it? Just to gain a few cubic feet of extra storage
space. . .