I have long questioned exterior tanks. I don't think they are a good idea no mater (climate) your location. If you ever try and sell a rig built for the warm climates to someone in the Midwest that would be the 1st objection.
However I would strongly recommenced a grease trap that goes in-between your sink drain and your waste tank. It will catch those small chunks of junk that will eventually clog up your waste water outlet. And I strongly suggest a wall hung shop vac that can be used to clean out any tank, steam table water and big spills. If you’d like you can see it in the interior picture of my trailer, on the left side just to the right of the door. It’s right below the fire extinguisher. www.DrofBBQ.com
It has a 14- foot hose I keep under the sink and it reaches most everything in the trailer. I will build both (shop Vac, Grease Trap) into my truck.