I'm doing a system almost exactly like sun's on my 97 dodge, but I'm thinking I might be able to do a looped return like chris from frybrid's easily as well.
I'm using the manual valves instead of solenoids. I already had one 4 way valve (1 in 3 separate outs) laying around, so my previous thought was to just cap one of the outputs off, but what If I use the 4-way valve on my return side to have 1) return to diesel tank, 2) return to veggie tank, and 3) return to just after my veggie filter (my looped return)? I don't see any reason it wouldn't work, but I wanted some input before I do anything too rash.
Also, a little help on how to deal with the tee off the return line just past the injectors that goes to the diesel filter would be appreciated, since I still don't understand exactly where that needs to tee back into the system.