It's a good idea to add an odor control chemical to the gray water tanks too. What goes into gray tanks doesn't naturally stink like what goes into black tank but after a while soap residue as well as the food particles and grease that find their way into the tank will ferment and/or turn rancid.
Some gray tanks can end up causing more odor problems than black tanks.
Over the years I've found the cheapest product sold for gray tanks does a fine job and they usually have a strong Citrus smell when packet is opened but a non-issue when rinsed down the drain. I put some of the packet in each drain, kitchen and bath sinks as well as shower drain. Then pour a couple cups of water in to rinse down and make sure it dissolves. This allows the stuff to work on whatever has accumulated in the P-Traps and eventually it all ends up in the tank.
"A wise man can change his mind. A fool never will."
"You only grow old when you run out of new things to do"
2018 Flagstaff Micro Lite 25BDS
2004 Nissan Titan