I do a lot of oil painting and as the brushes can cost up to £20 each, I make certain they are cleaned properly.The same method is used for any DIY brush. First remove as much paint by scraping the brush on the paint tin, and then remove more paint by wiping on newspaper or kitchen tissues.
At this stage they can be left in white spirit if you want to, making certain all the bristles are covered by the liquid, until you are ready to clean them. I personally continue cleaning, first by swirling the brush in the liquid and if necessary a second container of clean spirit and then rinse in cold water.The next stage, in my opinion is the most important, put liquid soap in the palm of one hand, I use Fairy Liquid, and move the brush in the liquid forcing it through all the bristles and up into the ferrule[ the metal sleeve holding the bristles]. Rinse the brush in hot water and then cold running water. Finally, remove excess water and allow the brush to dry naturally, although it can be left over night in a warm airing cupboard. I have used this method for many years and my brushes are still like new. One other thing if you have finished painting for the day and intend to continue the following day, cleaning isn't necessary, wrap the bristles in cling film or foil, this will keep the paint soft over night.