Every time I use it. I'm very tidy.
I put my tooth brush through a thorough cleaning after every use and I replace it often.I also floss a couple times a day.I have super clean teeth.
I buy a new one every couple of weeks ! So, never ! - Why not ? They're so cheap !
I'm downunder with you !!! ... It's still cheap ... 50 cents a week ! - I can get 'em for a dollar where I am ...
I rinse it out everyday, and replace it every 2 to 3 months.
When's the last time you checked your turn signal fluid?
Everytime I use it,and replace it every month or so.
I clean it after every use, your mouth is full of germs, yuck.