Anyone tried washing their seatbelts?

As above. The lad who owned my car previously was a mechanic and I am guessing he used the car straight from work so there are some grubby paw marks on the seat belt. Has anyone ever removed them to clean them? Or is it easier to do in situs? If so any tips? Thanks!
 
Just do them in the car. Pull them all the way out. Use washing line pegs to stop them retracting. Abit of washing powder in a bucket. Leave them to soak in the hot soapy goodness. Then scrub them. Job doneee.