@Elizabeth1880 There's nothing about the words"rustic", "farm property", "livestock" , "lots of dogs and cats" or "We maintain a composting toilet" which tells guests who have never used a composting toilet before, anything about it or gives them any idea about what is required when using one.
Instead of "we maintain a composting toilet for you", I would say something along the lines of "The toilet may not be a type you have ever used before- it's a composting toilet which requires that you spray out the bowl with vinegar after use, and throw all used toilet paper in the basket provided. This helps us maintain our eco-friendly, self-sustaining lifestyle. If this will be an issue for you, please do not book this property."
I would re-terate this in a message to guests when they request to book.
There's not much you can do about people who will book anyway, or think or say it's unsanitary. The average person isn't particularly adaptable, unfortunately. And if it were me, I'd tell the guys to just pee outside.