We don't have winter really but I do like to have the black tank good and clean once in a while. I tried those things that you attach to the bathroom sink and stick down the toilet but I haven't had a lot of success with them. Here in South FL we get sewer bugs if we don't get them clean enough. I tried a lot of things. I finally decided to try the GEO method.
I will admit that I had always considered this a form of Voodoo. It works! On the way home from the last trip of the season I use the geo mix. I fill the black tank half full and pour in the softener and the laundry detergent. When we get close to home I dump, fill and dump. Then put in a bit of water and some blue goo and things are fine.
There are a lot of other things in the article like using a clear pipe, Clorox and a lot of theorizing. I just use the softener and the detergent and it works. Easy too. First time in years I have seen my gauges work.