Wastewater heat exchange is not a new concept. Here's a 1986 paper on it. http://www.gfxtechnology.com/Pravda.pdf
The GFX "falling-film counterflow" system is mounted vertically, in-line with the plumbing drain, and has a wide-bore drain pipe. It seems to me that this is inherently less prone to clogging than the horizontally mounted Ecodrain would be.