I installed Vetus flexible black water tanks in my moody 376 for this season and connected them in with tec tanks electric masceratordischarge pumps which use the narrow bore pipe. It was all really easy and straightforward to install and so far has been completely odour free and reliable. I see no reason why it should not continue to be reliable as long as long as the only things tthat go into the system have already been through someone! For an alternative good Vetus quote try Heron yacht services +44 (01206) 303695 Good luck.
I have had a tank from Tek-Tanks twice! Once a standard one in my Fulmar, now replaced by a Dehler 36 so also for that. For the Dehler I made a wooden plug and took it to them and they produced the tank with all fittings welded according to my marks on the plug. Two outlets, one for Marina pump-out and one with a macerator to the through hull fitting. Pipe runs mean the Dehler tank is in permanent use as I could not fit a valve in an easily accesible place. One is there for use in the event of a major problem but is at the bottom of the cockpit locker. Go and see Gary on the Tek-Tanks stand at the boat show.
ITT Jabsco do a nice little, very rigid, 6 gallon, oblong jobbie, which will probably fit into a locker close to your heads compartment, so will not need complicated pipe runs. It is perfectly adequate for a couple and very east to link up to pump and outlet because all the outlets are already set into the removasble, top mounted hatch