Emptying black and gray tanks

Our 179 has a different system for emptying tanks than we've used before.  With our former trailer both tanks emptied through the same pipe, just different valves. The 179 has 2 separate pipes, so the drain hose will have to be moved from one to the other.  That raises a question:
Should we be concerned about transferring the bacteria from the black tank to the gray tank by using the same hose?  Or does it seem sufficient to just use a separate connector for each tank but the same hose?

always dump the black tank first.  then the gray water will wash out the hose and fittings to some extent.  We still wash out the hose and fittings with clear water when finished.
Vann

Yes, I assumed we would do as always - black first, then gray, even though we must move the sewer hose from one drain to the other.

Thanks for the link Grandpa Hiker!  Hoping the handyman in our house (not me) is willing to set this up and make dumping simple again.

 The drain pipe from the grey water tank does slope down to the double valve which is installed at the black water tank, however if the area at the dump station slopes down toward the rear of the Pod, the connecting pipe may not fully empty but over the  last 2 years (since I installed the double valve) having a little water left in the grey tank has not caused any problems.