I use my rv about 1 week a month and keep it at an RV park. When I leave I dump the black tank, refill it and then dump it again. Then I pour some pinesol in the tank and fill it again, then dump it again. Then I fill it with about 8 to 10 gallons of water and add the chemicals. For the grey water, I dump it after cleaning the black tank and refill it with Pinesol added, then dump it again and refill with about 8 gallons of water with some Pinesol. I also add some Pinesol in each of the sink/bathtub drains. Using this method I have had no black/grey tank oders in the two years I've owned it.
For your situation, I would attach the hose to the black tank rinse and get it as clean as possible. Then add some Pinesol and rinse it again. Then add fresh water and chemicals. The grey tank I would fill and dump it several times and then add the Pinesol to the tank and drains.
This is the task that takes the longest for me before I leave and go home, but I never leave anything but fresh water and appropriate chemicals in the tanks when I leave and it has worked well for me.
Good luck.
