10 seconds could well be too little. I would probably take 3 times that, but I've never timed it.
You want the brush to be clumped together with soap, really thick with it. The tip about putting a little hot water on there is a good one, it softens up the soap nicely.
Option number 2 is to pick up a cheap cream, it's easier to add cream if you use too much water, or didn't have enough in the first place, that is more difficult with soap.