Ah man, your killing me! I thought the 3rd valve thing was my idea. ;)
I use mine exactly how your wrote; backflush black (50 gal) with grey (60 gal).
Last weekend I did a little experiment. I dumped the black and used the on-board flush thingy to rinse my tank for probably 10 minutes.
Then I used the grey tank to back flush the black tank.
I was amazed at how much more "stuff" and toilet paper came out. I even went in and asked the family if they were using it - they weren't.
After flushing it once with the grey and dumping the black, I used the remainder of the grey (probably 15~20 gallons) and flushed the black a final time. I got a little more out of it.
So the 3 valve system works better than tank flushers or anything else IMO. It seems that sudden backwards in-rush of gallons of fluid really churns things up n there.
One of the best parts is you can do this at a dump station and it only takes 30~60 seconds.
Scott
