I left the bins only half cleaned. It was too hard. I will give them another cleaning on a hot day. It was a mistake to do it today, there is mud everywhere and the sun is not out to dry them quickly.
What I really need is a pressure washer, there is some very difficult brown slurry stuck to the inside of both bins.
I will have to get the big bad scrubbing brush out next time. Real elbow grease required. The overnight soak had very little effect.