I recommend that you clean your paint brushes very carefully, so that you can re-use them, and so that they remain in good useable condition.
It is crazy to have to buy new paint brushes continually, especially given the cost of good quality items. So cleaning them when you have finished using them, so that they can be reused next time, is really important.
Conventional wisdom suggests that cleaning paint brushes is best done by rinsing and re-rinsing paint brushes until the rinsing solvent comes out clean, without bending the brush, in an old paint can or bucket. Then the brush should be dried by hanging it, not by shaking it, before it is stored.
If you are in the habit of doing this, or have at least tried it, you will have found that, unless you do it properly, you might as well save your time and throw the brush in the trash. And to clean the brush properly takes a good quantity of thinners, and leaves you with a dirty container or bucket and lots of dirty thinners to dispose of.
Consider a cleaning and storage system where you simply put your dirty paint brush into a specially shaped container, which minimizes the amount of thinners that you need, and seal it. Agitate the container to clean it, and the paint brush can then be stored in the same container, ready for use again when you need it.