After mineral spirits I have had good success using Ivory soap and water. I now use foam brushes and get finish every bit as good as a quality bristle brush.

> In addition,I'ver been cleaning the brush with a degreasing cleaner and
> water,such as Simple Green,then rind=sing it well in water,and using a
> brush cleaning comb to straighten the bristles. Wrap in newspaper,and
> store on its side.I have the same varnish and paint brushes since
> 1967.Note that after a lot of use,the varnish brush will be demoted to
> paint.If you do this,it pays only if you use the best badger or china
> brushes.