That's the stuff. They show a picture of it in the Thetford Electra-Magic owner's manual.
http://www.thetford.com/wp-content/u...c-Model-80.pdf
I guess there's also a green, non-formaldehyde version that doesn't work as well. I've never seen it, maybe it's the Campa-Kem? Anyway, get the blue Thetford Aqua-Kem...