why separate tanks for grey and black water?

dave17352 wrote:
I agree with all the posters here. Now on occasion I have equalized my tanks when I need more grey water room by opening the grey valve and leaving the black tank valve closed. This brings them to the same level.

I don't see how this equalizes the level. If you were to open both valves and hold the stinky slinky above the top of the tanks, then the fullest tank would sluice into the emptiest tank. Hopefully, the grey tank is fullest.:E

I do this to provide a little extra liquid to flush out the black tank. Be sure to hole the hose high.