Ivory is just a brand, every soap bar with lanolin will do.
I use soap bars, made for baby's to finish the cleaning of my brushes. I have only hair brushes. I always start the cleaning with special terps, without the odour, white spirit says the label.
In fact; first I remove most paint from the brushes with kitchen paper, than I rinse my brushes in white spirit that is already used once or twice, dry my brushes with kitchen paper, than I rinse my brushes in clean white spirit, dry with kitchen paper and than I wash my brushes whit that bar of baby soap.
I leave my brushes to dry, hanging in a brushes pot, with the hairs down:
http://www.schminkspecialist.nl/shop_images/737_0_large.jpgThat's how the least oil paint pollutes the lessest (drinking)water.
After a while, when the oil paint in the terps is all on the bottom of the bottle, I pour the once used but still very clean white spirit back in the botlle 'used terps'. I throw it away, we do have special chemical waste collecting over here, so the white spirit will be destroyed in a proper way.
You have to be very carefull with the pigments and rinse as less as possible into the water, it's easy to pollute water, it's not so easy to get it clean again.