If you heat water up in the kettle, pour in a touch of your usual shampoo and get an old towel or face cloth, dip it in the water and then scrub the coat in a circular motion. You don't need to rinse the coat and there is barely any excess water.
I do this after clipping all my horses as do my liveries and you get a lovely soft, clean, shiny coat at the end. It only takes about 5-10 mins!