I have the fresh water Marine Elegance toilet with the Purasan treatment system. I installed the Purasan when I had to replace a leaky holding tank. The tank is still clean since I will only need it in discharge restricted areas. The Purasan uses a large chlorine tablet to generate a small amount of chlorine with each treatment cycle so the sterilized waste can be discharged. It's less than a year old but works great so far.
I've followed the Head Mistress, Peggy Hall's advice and had good luck. I just found out that she has retired but lots of good advice is still available in the archives of her forum.
The Head Mistress: Flush with the joy of retirement - SailboatOwners.com