You can use Listerine in your Waterpik however it's not recommended to use straight Listerine in the Waterpik as it could damage it.
You should at least put half water and half Listerine in the Waterpik which dilutes it and so it doesn't harm the Waterpik.
But you can try putting some Listerine in your Waterpik without diluting it first and it should work fine as I've read online that some people have used straight Listerine in their Waterpik and it has not harmed it.
But the manufacture of Waterpik doesn't recommend it and it could void the warranty if you do.
When I use Listerine in my Waterpik I dilute it with some water to make sure it's not too strong so as to damage it potentially.
Using a Waterpik is good to help keep your teeth clean and helps to clear food debris from your teeth but the Waterpik does not replace flossing.
When you use the Waterpik to clean your teeth you still should use floss and do flossing at least once per day especially after eating a meal.
The Waterpik is pretty good at getting most food particles out of between your teeth but I noticed even my Waterpik leaves some food particles behind so whenever I use the Waterpik I also floss afterwards to make sure all the food particles are removed.
I still find traces of food particles in between some of my teeth after using the Waterpik but the Waterpik does remove most of the food particles.
So you still should use floss at least every few days or so when you use the Waterpik.
Flossing your teeth at least once per day is very important at keeping your teeth clean and healthy.
Brushing your teeth is better than not brushing or flossing at all but even when you brush your teeth there still can be food particles in between your teeth as you chew the food and sometimes those food particles get stuck between your teeth.
Those food particles can rot and lead to bad breath, gum disease etc and then can also lead to tooth decay as well.
So flossing at least once per day is needed to keep your teeth healthy.
To keep your teeth clean and healthy and to prevent gum disease you should floss at least once per day between tooth brushing.
Some people including myself floss their teeth twice per day such as after a meal such as dinner and then again before going to bed.
I used to only floss at night before bed and after taking a shower but I started flossing my teeth after I have dinner and then floss between my teeth once again before bed.
I've noticed my teeth are much healthier and have stayed cleaner as a result of flossing twice per day.
I brush my teeth twice per day and also floss my teeth twice per day as well.
As long as you floss once per day that's usually good enough but flossing more often is not bad either.