My son and I created the "Decopus".  A 10 legged monster that was annoying to make, but should make life pretty nice.  The 2 valvues are 5 way valves.  There are 4 lines in, with one out. (or 4 out and one in).  This will be where we control our water distribution on the boat.  The top one will be the "in".  One line from each tank (3), plus an extra that can be put into a bucket, or anti freeze, or a 5 gallon water bag for a short weekend trip, etc...  This will lead to the pump, then the filters, then back to the other valve.  This will then have one line out to each tank, and one to the "Boat".  When it is on "Boat", the boat will be operating as normal, with water out to all the taps, etc...  But if I want to move water from one tank to another I can.  And with the added bonus of going through the filter in the process.  Or if I just want to equalize the tanks, I can.