duel 3" sewer connections using a Sewer Solution?

I have not had to deal with your setup but I do use the Sewer Solution. I would think you would need two sewer solutions on the black tank drains and just a simple gravity hose to the gray water drain.
I'm guessing that it would be easier to just drain each hose one at a time rather than trying to retrofit a T or T's. You probably only need to drain the blacks once in a couple weeks, takes me three weeks but you would need to have a continuous flow from the gray tank.