Perhaps the salient points from this, and the microbiologist thread should be consolidated into a sticky?
i.e. keep it dry, don’t stick anything but water in it, mild detergent first, baking soda next, commercial tablets (or baking soda and very dilute bleach;same as the tablets) if you forget about it and it gets funky… And of course, rinse it well, and try not to forget it for a month (in the back seat;in the closet;in the cabinet;whatever)