Just for the halibut, I thought I'd tell y'all about the so-far very satisfactory experience with our C-Head composting head- or moldering head, as the manufacturer prefers to call it. This is a fine example of what happens when an engineer with a good practical bent considers a problem from scratch, rather than starting with preconceptions.

The C-Head box arrived within a couple of days of our $500 order, most expertly packed. The installation and use instructions were outstanding, and it was ready for use in about 15 minutes. Of course, to rig up the fan and ventilation hoses, tie-downs, etc, will take a very little bit longer, but for right now, it's been just fine for 6 months of light use. We spent every night this past week aboard with two small boys, and it all worked just fine.

1. This thing works by separating liquid waste from solid waste. This assumes that ALL users will sit to pee. The design of the bowl, with its funnel to the front and a ~5" open chute to the rear, directs urine forward into an ordinary disposable gallon plastic jug, and feces to a bucket containing peat, sawdust, or, best, coconut fiber (coir), and a crank-turned paddle, which churns the contribution, to coat it with fiber and dry it out. We empty the urine once every day or two, rinse out the jug, and put it back in place, or toss it and put in another clean -and free- empty gallon jug. Every week or two, with regular use, we'll dump the peat/poop mix into another container until time to dump the odorless dried lumpy stuff either into a plastic bag for the nearest marina dumpster, or add it to our dedicated-to-ornamentals compost pile.
2. There is no plastic hose to permeate with sewage-smell. There is no big sloshing tank of waste and chemicals to pump out. There is no complicated/delicate mascerating apparatus. We do ask that nothing but small amounts of TP - and, of course, human waste, go into the toilet, but it's not a huge clog-up maintenance disaster when a guest doesn't listen. It just all gets dumped in due course, along with the coco-fiber-etc. The head has no odor, except, perhaps, a bit of peaty-mustiness. No stink at all.
3. Some composters are huge and ungainly, but the C-Head is reasonably small, about the same height we are used to at home, with a narrow footprint. In our houseboat, it fits snugly against an exterior bulkhead. Its capacity is less than some other composting head, but that just means we may have less trouble with wee insect-beasties than some composting heads apparently can, as it is dumped more often, before they can hatch. (That is a reason for going with Coir rather than the sometimes troublesome peat. Plus, coir, unlike peat, is a renewable resource, and comes in very compact bricks, and a whole season's worth will fit in a shoebox.)
4. The manufacturer offers a number of exterior decor options. We went with plain-old white, but if you have a hankering for burnished teak, mahogany, or glossy black, that can be done. I ordered an elongated seat, but shouldn't have. The round seat we replaced it with is just as comfortable, takes up less space, and fits better. It's also a bit less expensive.
5. The whole thing is simplicity itself to keep clean. The milk jug, and the poop-bucket each lift out and reinstall very easily in one easy motion, without dismantling anything. For cleaning, all is necessary is a damp rag for the exterior, and if necessary (we haven't found it so, yet), a good rinse-out of the waterproof interior and the poop-bucket.

So far, we are exceedingly pleased, especially after hearing all the stinky horror stories of conventional marine heads and holding tanks. This gadget is cheap, durable-looking, easy to deal with, and entirely stench-free. What more could we ask?