All you need is two jars, clearly labelled. Let me explain in more details…
Take a clean glass jar with an opening wide enough to fit your brush. Fill 1/8 to 1/4 of the pot with white spirit and clean your brush as usual (I just remove as much paint as possible with some kitchen towel or newspaper then squash the bristles a few times, in various directions, against the glass so that the white spirit can reach all parts of the bristles). When finished, close the lid tightly and put the jar away on a shelf.
When you next need to clean a paint brush, you will notice that paint sediments have fallen at the bottom of the jar, making the white spirit clear again. Empty the white spirit into another jar (labelled “white spirit cleaning jar”) and clean the paint brush inside the new jar. If you used the first jar, the sediments would stick to the tip of the bristles making cleaning very awkward.
When finished, pour the white spirit back into the first jar (labelled “white spirit storage jar”) so that the paint sediments can collect on top of the previous layer, keeping the second jar sediment-free. Store both jars next to each other until the next cleaning job.
This method will enable you to reuse the same white spirit many times and save you lots of money!