Hi,
Nice simple setup.
I'd really like to hear how it works out.
Maybe you can measure the temperature of the incoming and outgoing fresh water and get an idea how much of a preheat you are getting?
I've heard that grey water gets pretty smelly after a day of sitting around, but I guess that this might not matter since its all enclosed.
There are a couple articles on grey water heat capture here:
New and experimental solar projects and concepts* for do it yourselfers
The first one is one that Nick Pine and I worked on, but eventually pooped out on. The "Canada Study ..." is a good one.
It seems like the whole idea of recovering heat from grey water does not get enough attention, and that there ought to be a simple way to do it -- maybe you have found it.
Gary