The only restrictions we've ever encountered when hooking up to a campground sewer system were notices that products containing formaldehyde were not allowed. I believe that the Thetford Campa Chem Natural products are formaldehyde free, this is what we've been using for years.
Camping World seems to have more than one product that is formaldehyde-free:
http://www.campingworld.com/search/i...d&Nty=1&Ntpc=1
If in doubt, call the campground to see what their restrictions are.