Black tank drained/flushed and a couple or 5 gallons of water with treatment; grey tank empty, fresh tank empty, no gas treatment.
Note black tank will still smell when you return to coach, add treatment right away and it will knock the smell down.
I have left fresh water in tank, depends if it has residual chlorine after a month or storage. We use our fresh water for washing only; we use RO water for drinking.
Towr: 2007 Country Coach Allure 470 - 37 Sunset Bay Cummins 400 ISL
Toad: 2007 Jeep Grand Cherokee (yes, it has a Hemi)