I’m not an expert – just experienced
Here is a sewer hose that will drain completely
photo from twopennytravels.com
Here is a sewer hose that will
not drain completely and will freeze
in the winter.* photo from RVTravel.com
You may wish to put insulation around the waste hose to give the fluid more time to drain before the freezing temps cause a problem. I have seen people add heat tape to the drain hose also. I do NOT recommend that. Heat tape works fine on water lines that have water in them. Full lines are less likely to over heat. An empty sewer line may melt or scorch from the heat of a tape. There MAY be tapes made for this purpose, however I’ve never seen them.
Frankly, if the sewer line has the proper decline it should run fine except in the very, very, very, coldest weather – when you are not going to go out to empty your tanks anyway.
One last thought on sewer lines. If you are really concerned that they may freeze, add some RV/Marine Antifreeze down the stool. Make sure it is RV/Marine Antifreeze and not engine antifreeze. You can find it a almost any auto parts or home store like Home Depot, Menards, Lowes or even your local hardware or grocery store may carry it if you are in an area where it is demand.
*About the hose that will not drain properly. To be fair, that is what the person was trying to accomplish. By forming this "P-Trap" in the line they could leave their dump valve open all the time without sewer gas entering their RV. You could certainly do this where you need not worry about freezing temperatures. However, if it freezes, it will block the flow and possible rupture the hose.
(Next topic; Water In – Fresh Water)