I am always reading how people are unable to get rid of dust in the horse's coat.
Think about it! What lays dust?
Simple answer - water.
When grooming a horse as opposed to bushing it, you should go all over with a rubber curry to raise the grease and dust, you can flick the worse off with the dandy brush but the hard work comes with the body brush.
Starting at the neck, standing facing the horse's quarters, brush in the hand nearest the horse, left hand on the left, right on the right, and a metal curry in the right, start to brush using your weight to push into the horse.
Before you start dip your fingers into his water, sprinkle a few drops onto the body brush and rub them all over the brush which should be damp not wet, and start brushing, four strokes to each area using a circular movement. Clean the brush on the curry regularly and keep dampening the brush. Every now and then knock the grease out of the curry.
Once you have been all over the horse get a stable rubber, an old piece of towel or thickish cloth, make this into a wad and slightly dampen this. Go all over the horse with the cloth again working in circles but finishing with the hair.
This will give the horse a good shine, lay the dust and give you a good workout!
A horse with regular grooming will not need show sheen or bathing.