Every time I am doing a workshop I have been asked how to wash the brushes after painting with oils. I don’t use turpentine in my painting process nor when I am washing brushes, but I am not saying don’t do it. Just make sure that after cleaning them with turpentine, finish cleaning them with a soap and water.
If you are painting with regular oils, you can simply soak them in hot water with little bit of washing powder. Make sure that just the bristles are dipped in the water, avoid soaking metal parts of the brush because they might rust especially if you’re using them very often and leave them for too long. I would leave them over night or at least a couple of hours and then using washing soap like sunlight soap wash them under the running warm water. If you don’t have washing soap, regular cake hand soap can do, it might take a little bit longer. Once soap is clean of paint you can check by rubbing the brush on old rug. If there are no traces of paint you can dry them. It is very important that brushes are cleaned properly, if not they will be hard and not usable. You can simply fix this if you put them back in a hot water with washing powder and leave them to soak for a couple of hours and rewash it with soap and water.
I usually leave them on the sun or in winter put them in the front of heater. One important thing: if you are using natural hair brushes I would wash them straight away and not soak at all. Especially hog or sable bristle brushes which will literally melt into a slimy mess.
Using fine brushes with long hair could be a problem to soak because they will curl or bend and there is no fix for that (as I know), unless you have special device that can hold them you can simple tape them with the larger brush so the tip will be in the water but not bend.
If you have brush which you by accident left to dry, simple leave it soaked for a couple days and then wash with the washing soap. You can also use dish washing powder for that which is much stronger. Alternatively for fine brushes with natural hair u can boil vinegar and keep dipping them and wiping with dry cloth. I also found that you can also dip them in linseed oil and wipe number of times. Be patient it make take quite few times of dipping and wiping. ALWAYS finish by washing them with the soap.