[Diaz Dezine]

I agree with KD. If your paint is waterbased it may not mix well with anything solvent based and it may not clean well with the paint thinner that you are using, it will gel or get all clumpy.
I have heard that some people strain there paint, especially if it is waterbased, through some kind of strainer, like a piece of panty hose.
Make sure you are cleaning your brush with something that is compatible with your paint.
Hope this helps.
DIAZ