The blurb on the back of tin will tell you to wash your brushes out in meths. Don't. All it does is dilute the BIN paint. A better option is to buy some household ammonia. It is alkaline and dissolves the paint. I cut up a plastic milk bottle, pour a little ammonia in, agitate the brush and rinse in the sink. If the brush has gone hard, I leave it in the ammonia over night. Because of the smell I leave the ammonia tub outside. In the morning the ammonia has evaporated off and I am left with water and dust at the bottom of the container which can be poured down the sink.
BTW BIN is available in spray tins if that makes life easier. The nozzle does tend to clog a lot so use a cloth dipped in meths or alcohol to clean it periodically.