Hello. We have a Nature's Head and for us, a composting toilet works well for us and suits our style of travel. However, it is not for everyone. If your AI has a wet bath, I would not recommend installing a composting toilet. All the moisture from using the shower would not be good for maintaining the correct moisture content in the solids receptacle.
If you just got this unit and the black tank stinks, the previous owner probably didn't practice good tank management. They may have had a practice of pulling up to a site, hooking up the "stinky slinky", opening the valve, and just letting it drain as they used it. The problem is the liquids drain out, and the solids pile up and remain. You might be able to shine a flashlight down the toilet drain and see what I'm talking about. There are lots of ideas on this forum about how to deal with that. I recommend getting a natural tank digester, putting it in, filling the tank with water, and letting the digester do it's job for a couple of days. Then find a dump station where you can hang out for a while or a full hookup site. Dump the tank. Use the tank flusher to nearly fill it, then dump again. Repeat several times. Hopefully you will see solids floating out when you dump. Then put more digester in and start this process all over again. You may have to do this several times until your tank is clean (no more "floaties" coming out...).
If you think you want to go the composting toilet route, think about what sort of camping you are going to do. A composting toilet allows you to avoid dumping for 2-3 weeks. This is great for boondocking. But there are pros and cons. If you don't need to go long periods before dumping because of your camping style, then it probably doesn't make sense to spend the money. Just my $.02.
My guess is you just need to do a good tank clean and then use a good natural product and follow good tank management practice to keep it clean.
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