But im intrested to use to clean my brush wile im painting like morgan do
In that case, make sure you use a drying oil like linseed, walnut, safflower, or poppy. Non-drying vegetable oils or mineral oils could cause drying problems with your paint if enough was left in the brush.
I pretty much use the same oil medium that i paint with (walnut oil atm) to clean my brushes while i paint. If i need to alter a mixture and don't want to get a new brush, i dip it in oil and wipe it clean. There won't be any paint left on the brush to interfere with my new mixture.
I don't know who Morgan Weistling but this method is common among most of the painters i know.