Every day, always, for nearly 40 years. It was originally a prescription from my ENT when I had very sticky mucus and repeated ear and sinus infections. When he punctured my eardrums to insert tubes, the mucus was so fluid was so thick it didn't drain and he had to suctin it out. I hav occasionally runt out, and after 2-3 days my mucus starts to thicken again.
For thos ho may wonder - no, it is not Cystic Fibrosis, I was tested.