Yes!!! I am so there too! I tell people this happens to me but I haven’t written about it yet. There are little things like this in my writing process that I hadn’t realized until recently. Then, after getting a few ideas in there in a row, it clicked.
For me, showering, or for me it happens when I brush my teeth too, it is a moving meditation. I’m still processing and somehow stepping away and moving makes it better. I worry about them going down the drain as you say. I end up just reciting them and creating little memory devices on the spot. Wow, it’s cool, and refreshing, to read this happens to other people too! Thanks for sharing.