My off-road POPUP trailer only has the fresh water tank and the Suburban SW6DE Water Heater.
I open the HOT and COLD Spigot at the sink and also open the HOT WATER relief valve and drain everything through the LOW POINT water drain valve... It does leave about a 1/2-inch of water in the bottom of the hot water tank. Actually about the same amount of water even if you drain from the bottom port of the hot water heater...
My fresh water tank drains completely through the LOW POINT drain valve.
We don't consume anything from the fresh water tank. Always bring along bottled water for drinking and cooking.... No real reason just got in the habit of bringing along a couple of bottle of bottled water... WE also freeze the bottled water and then sit them inside the small fridge on the day of the trip to help get the fridge going quicker when we arrive at the camp site....
It has never been a freeze thing for me of having alittle bit of water remaining in the bottom of the Hot Water heater as there is alot of expansion room inside the hot water tank for any ice that might form...
My bottom port is also where the ANODE ROD is located. I do look at it once a year usually at the end of the camping season for me. This is usually the only time I will do a good water tank inspection. I just hate to have to remove the bottom port of the water heater just for draining water... Just let it drain out through the water system works good for me...
Roy Ken