For window seals, to keep them soft so they seal better—and to ensure that windows don’t get “stuck” to them.
This stuff is powerful and one can treats a whole tank. I use it every once in a while—and just before long term storage—to give the holding tanks a good strong cleansing.
This is one of the first things you should install if you have a new RV. It allows you to quickly winterize your pipes by giving you an easy valve and hose through which to introduce antifreeze. Cheap, and saves a ton of time!