Finally cured my bad breath after 18 years!
I have had chronic bad breath all my life. No matter how much I brushed my teeth or cleaned my tongue (2 times a day), no matter how many mints I ate or how much water I drank, it was always there.
It turns out my bad breath was caused by a mix of the below three:
Acid Reflux - I started chewing my food properly, taking fennel seeds after every meal, rinsing my mouth after each meal, and taking 5-10 deep breaths after every meal. Also included more probiotics daily.
Sinus Issues - I've had nasal congestion since I was a child, and post nasal drip. Turns out the Acid Reflux was what was causing the drip. I also started taking a drink with ground turmeric, black pepper, and lime every morning, which helped a lot.
Dry Mouth - A dry mouth can lead to less saliva, so food particles and odor stay in your mouth (saliva is a natural mouth cleanser). My dry mouth was caused by mouth breathing. I used to find myself breathing through my mouth during the day and at night. Also started drinking a lot of water!
If you keep your oral hygiene in check but the bad breath keeps coming back, hope this helps! The solution may be completely different than just "cleaning your tongue" or "brushing twice a day."
They're important, but may not be the actual reason.