Did this the other week. Used AutoGlym interior shampoo and warm water. I pulled the seatbelts out of the car untill they stopped. Then soaked the belt with the autoglym, and kept running my hands up and down the belt (ooo er) Kept doing this, and then dipping it into warm clean water in a bowl ouside the car. They have came up supurb, they were really grubby too!! Well chuffed. To dry them i used an old megures car towel to soak up the excess, then just left them plugged in over night and the next (hot) day. Perfect now.