This topic will be of no interest to any land based readers, so feel free to x out this right now. But for sailors, especially those who live on their boats, and especially those who live on their boats in foreign waters, this topic is very important. Every week or two I get someone sending an email asking about it and I've been putting a lot of them off, so hopefully this addresses everything in one swoop.
In 2007, I removed our first head. A manual "wet" system that had a big ass holding tank.
Still in 2007, we then installed a Lavac. Another manual "wet" system, but more durable and with less moving parts.
In 2010, we ripped out the Lavac and installed a Nature's Head composting head. With it went the 25 gallon holding tank and all the hoses. We plugged all the various holes through bulkheads and two thruhulls were shut, their bronze barb fittings staring up unused in the bottom of a compartment.
In 2012, we threw the Nature's Head into the trash and put a Raritan SeaEra electric "wet" system in place with a fairly straight forward holding tank. The head discharges into the top of the tank which sits above the waterline, and there's a single drain hose from the tank to a thruhull fitting. In the right setting we keep it open, in the wrong settings we keep it closed. Regarding the "complexity" of an electric unit, there are a gazillion other moving parts on a modern boat so the religiousness by which some folks want to stick with manual is beyond me. It's noisy, but you get used to it. It's also easier on the plumbing and you can use normal toilet paper.
Here's the details:
The Nature's Head is terrific, but we had a massive bug infestation. Mind you, this is after we used it successfully for nearly a year. We're not filthy people, we followed all the rules, but at the end of the day you are creating an environment that is perfect for organisms to flourish in, including disgusting little bugs. Once they are in, they are extremely hard to get rid of. Very few boats have this problem. We have a friend who got hit by a whale in an anchorage: weird shit happens. For us, we experienced a huge bug infestation and I didn't want to go through it again. We're talking about millions of barely visible white worm like creatures all over the boat.
Other than the bug problem, the Nature's Head was terrific and we would still be using it today. If you live on the boat the solids compartment will not be composted fully and chances are you'll be staring directly at a turd or two. But there is no smell, it's extremely benign, and even emptying the wet container every day or two is no big deal. Just don't spill when moving it around through the boat in a seaway (ask me how I know). Regarding throwing solid waste in the trash, I've heard people call human feces "hazmat". Well, take a look at what a diaper has in it from every human child.
The Lavac is terrific but in a holding tank environment it pumps A LOT of water so you will either a) scale your hoses by not pumping enough or b) fill up even a large holding tank quickly.
Regarding holding tanks, let me be honest and tell you over the vast majority of the world pumpout situations simply do not exist or happen. After having been in Mexico I've seen a lot of boats, hundreds by this point, with folks living on them that rarely leave the slip. No one is pumping out. They dump the tanks at night. No one will tell you this. The marinas want to pretend that no one does it because it's gross, owners don't want to get in trouble, and no one wants to be the guy in the room that farted. But it's the reality.
The reality is that with a blend of judicious holding tank use, shore facilities for the dirtier of the two human movements, day sails, and outbound tides at night, you can be a fairly responsible citizen regardless of whether or not you're in an area that has pumpout systems. And again, the odds are about 10,000 to 1 that you'll have access to pump out systems.
I'm disabling comments on this entry because I don't want to get into an Internet argument about pumping crap overboard, whether or not we should have used COIR or peat moss, or whatever else people can come up with. We have a holding tank, we use it. Pump out systems don't exist in most of Mexico, and from the folks I've talked to in the South Pacific and Asia you'll find nothing there either. In the Med and other heavy areas of "yachting", I'm sure things are little different.