Our playgroup put theirs through the dishwasher and they come out clean, so if they are ones that can have a hot wash try that.
I used to fill the sink with water and gently mix the toys around (if that makes sense) and I also found they came clean. Sometimes had to change the water a few times. If they have dirt in the cracks use a toothbrush as it doesn't scratch.
To dry roll in an old towel then finish drying outside with a bit of sun on them.