Bucket of warm water with fabric conditioner in, and a stiff brush combined with elbow grease and mine come up nicely.
Not worth washing them though IMO. After 1 day at the yard they become grubby again
I wouldnt use water, stiff brush yes and a cloth. Then spray them once they are clean with that suede protection spray (can't remember the name) but next time the dirt will be easier to brush off! I have funky pruple ones!!!!! x x x
I had some shire ones put them in the washing machine on 40 degree cycle! Though I very stupidly put other things in wash with them and all the color ran now everythin pinky purple!