When washing sheepskin boots or footwear you need a delicate cleaner so as to not damage the upper. This is a mild shampoo used with cold water to remove stains. After shampooing fill up the boots with paper to keep their shape and help them dry.
It is good to have brush, not a suede brush but a firm nylon bristled brush to bring up the nap and soften and restore the finish.
Also, before shampooing use the nylon brush to get all the surface dust or dirt out of the sheepskin.
This cleaner would be fine to use on sheepskin slippers too.