I use 2 jars cold tap water, 1 with a couple of drops of a well known baby shampoo and the other just plain water. I found that dish soap (Dawn etc) seemed to dry out the bristles. The 1st jar removes the bulk of the paint, the 2nd helps clean the brush.
This has been my own method for 30+ years, except I lob in whatever detergent is there - shampoo, washing-up liquid, shower gel, whatever. The plain water in the rinse jar means you always have a supply of clean water to dilute your paint.
When done, I meticulously clean my brushes in spit, giving them a bit of a lick to force them into something like a point. If I can be bothered and don't just drop them and wander off.