I've had an Airhead since buying my R25 new, and thus since the holding tank was never used I repurposed it as a 2nd water tank. By fooling with the hoses to the new spare 30 ga water tank, I simply redirected the macerator pump outlet to a garden hose connector in my big starboard lazarette. By connecting a ten foot hose to that connector and passing the hose through the door into the cabin and out the window over the stove I can pump (via the macerator) water from the spare tank into the normal FW tank. Ranger positioned the FW tank inlet so it can be reached from the window, which is handy to pour a little bleach into now and then when the water gets smelly. Hence, I go around with 60 ga of fresh water.
I've done something interesting, which eliminated the only hassle with the Airhead, which was emptying the pee tank every couple days (if two people were on board). Sooner or later you're going to find it full in the middle of the night, and its an ordeal then to empty it. Kind of gross when people see you pour it overboard and guess what it is with the foam and all.
Anyway, Geoff will sell you a pee bottle with a valve at the bottom, and I found a snap on connector to attach that valve to standard vinyl tubing, thus you can easily disconnect (
http://www.omega.com/Green/pdf/QDFitting.pdf) the tube when needed. I hole sawed a 2.5" hole in the FG under the sink cabinet and using the deck plate under the sink for access ran the tube out along side the water heater into the lazarette. There I installed a small 12v pump. The tube continues around the stern and then up the port side of the boat past the batteries to the through hull that used to serve the macerator. I used some simple barbed adapters to attache the vinyl hose to the through hull fitting, and I even threaded the tubing through the old macerator hose-that protected the vinyl and reduces kinks which it is prone to. I find that gravity empties the tank, and at the end of a trip I pour half a gallon of fresh water (I have lots) into the AirHead and run the electric pump so urine doesn't sit in the tubing.
The AirHead is now perfect. I get an entire summer season on the solids tank it using the boat occasionally. The manufacturer says a couple will fill the solids tank in a month with daily use, but Mike gets 6 weeks using marina heads when possible. I met a couple on the St. John River in FL who live on their catamaran and use an AirHead. When the solid tank fills, he puts a lid on it (it comes with one) and bungies it out on his forward deck to allow another month of composting, he then dumps it on a garden somewhere and switches it out with the tank in the AirHead to start over. Geoff sells spare tanks and lids. Geoff even sells packets of enzyme to speed composting. You'll be in touch a lot with the manufacturer when you install the unit which argues for the AirHead as Geoff is responsive. The Nature's Head is a copy made by his ex-employees and I can tell you they either don't respond or don't know the answers to most questions.
No pump out, extra water (or diesel with an upgraded tank), no hassle. I've talked to the harbor master in Key West and he told me just dump the urine bottle over the side as urine is sterile and you won't find more paranoid people about their water quality folks then in Key West.
