for acrylic paint

I use hot water an dish liquid.

pour in half a cup of steaming hot water and drop some dish liquid in.

now dip the dirty bushes in and swirl it about.

Take out and use a cloth to dry it

for oil

I use the same, but I use toothpaste as well.

I take the dirty bush, swirl it around the glass, remove it and take a pea sized amount of toothpaste and massage it into the brush. Then I resoak it and clean it off with a cloth.

If the brush is still dirty, I redo it