Hey mate,
When you do the nasal rinse, do you tilt your head back or do you tilt your head forward?
What I have noticed is that a lot of people do the nasal rinse with their head tilt forward, and because of this, the saline solution only washes the front part of the nasal cavity, while leaving the back unwashed.
If we look at the anatomy of the nasal and oral cavity, the food that we eat (blue dots in the picture) goes through the oral cavity, and residues can and often get stuck in the back of the throat where there is a connection to the nasal cavity. All it takes is one microscopic food particle, and that's all the bacteria needs to grow.
Therefore, when you do the nasal rinse, the head needs to be tilted back so that the saline solution flows through the nasal cavity and into the back of the mouth to completely rinse away all the dirt, bacteria, and food that are stuck there. It will feel a bit strange, but you will get used to it.
Also, the best times to rinse is 1) after you brush your teeth at night after dinner, to wash out the food that gets trapped, 2) after you brush your teeth in the morning, to wash out the bacteria that was built up while you were asleep at night.
I used to have a pretty bad nasal infection with dark green phlegm, and all I did was using this saline rinse technique and I'm now nearly 100% normal without using any antibiotics.
Good luck, mate.