little surprise every time we dump the tanks

Durb wrote:
two posts here about using the gray tank to back flush the black tank. I am curious about this process and would appreciate some feedback as to how it works. What keeps the black tank from mingling with the gray tank innards?

Durb,
Hope this helps:
You need a 3rd valve that attaches where your black and grey tanks discharge at the same point. In the photo below "C" is my grey tank and "B" is my black tank, "A" is the additional attached valve with the clear section (Flush King).



Step 1:
Open A - the Flush King
Keep C - Grey closed
Open B - Black

Let black drain until nothing comes out any more. Water may run for a while, but wait for it to quit completely. You can see that through the clear section.

Step 2:
Close A - the Flush King
Leave open B (Black)
Open C - Grey

The grey water will now back flush into the black tank. Because the black tank has no liquids, nothing will ... or can ... enter the grey tank because of the force of the water from the grey now filling the black.

Wait about 5-10 seconds, or until you don't hear any water sloshing any more. In the clear section, you'll see water, but the valve there is closed.

Step 3:
Close Valve C - Grey
Leave Valve B open (black)
And now open A (the Flush King)

You close Valve C (Grey) so the black will not flush back into the grey. So close it before releasing the Flush King (A).

Step 4:
The black tank will flush more "stuff" out. You'll see in happen in the clear section. You'll be surprised how much more solids come out too!

After the water quits running from the black tank, repeat step 2 and 3 again.

If your grey tank is full, you can easily flush the black tank 3 times.

Step 5:
After you have back flushed the black tank (at least once, if not more, and you are satisfied) there should still be water left in the grey tank. The black is now cleaned out.

Close Valve B (black)
Leave Valve A open (Flush King)
Open Valve C (Grey) and use the rest to flush out the sewer hose. (E)

That's how you do it.

(If you have a Flush King, you can run water via an attached garden hose -D-. Leave the grey tank closed (C) and open the black tank valve (B). Turn water on to the hose (D), and fill the black tank (B). Drain normal, leaving the grey tank (C) closed).