Cleaning oil-based paint from brush efficiently
Traditionally, we would keep the jar still and covered and in some time the paints settle to the bottom and we’d decant or carefully pour off the top layer of clean solvent into a different jar. The crud that’s left in jar one can be scraped out with a stick, then wiped clean with paper towels or old rags - either can be a fire hazard so store away from the house in a steel can with tight lid. Re-use the clean solvent. I lightly push the brush into the jar which has solvent level == to about 3/4 length of the bristles. Dab and twist lightly several times, then flex the bristles on dry part of jar to remove as much solvent/paint as possible. Go to a jar with cleaner solvent. It takes two or three such steps to get most of the paint from the brush. I don’t think you can get 100%. The majority of the solvent is preserved and recycled. 

Oil painting and saving the brushes is a pain. Typically I don’t reuse a brush from dark or saturated paints with light colors on the next go around. Dry the cleaned brush as much as possible and store it with the bristles in the correct shape and wrapped with paper towels and a rubber band on the ferrule. It will get stiff but you can condition it just before use by working it dry or with a little solvent compatible with your paint, as you described. Good quality bristles will last a number of such uses.