I would NOT suggest washing brain tanned buckskin/leather, there is a home dry cleaning method that can be used successfully.
Brain Tanned hides, that are not smoked and are of the lighter shade, mostly white color, if the tanning process has been completed properly. Washing Brain tanned leather will lose the effect of the softening process, that was used during the tanning of the original hide. When dry, the item will become very stiff if washed. Brain Tanned Buckskin can be cleaned using Corn Meal and a clean brush. Recently to clean a baby cradle board, made with Brain Tanned Buckskin I used a new plastic net type dish scrubber, with Corn Meal it worked great. Heavy grease will not come out, but the area can be cleaned up some using this method.
Moccasins Tanned in the Indian way, Brain Tanned, are a different story, when they become wet, you must wear them until they are completely dry in order for them to remain soft & still fit you the same as before they met up with water.
Its odd how teachings from ones youth, can totally slip away and suddenly, after 50 years, one's brain has recall of the words & lessons taught by wonderful elderly, Native Indian ladies, now gone from this earth, they really knew how to create works of art, others will cherish for generations, if cared for properly. During my youth, I only remember Indian Dance Outfits, nearly 100 year old, Eagle Feather Head dresses, Buckskin clothing being carefully wrapped in cloth with some kind of dried leaves, then stored away in trunks. I wish I had asked what these leaves were? others of my people should be able to answer this question. Obviously this method of storage, served its purpose well, many beautiful Native artworks, of days, past show up on ebay, looking well preserved.
Commercial Tanned Leather, of suede can be washed very successfully in a washing machine with warm water or cold. During the rinse cycle add Fabric Softener. After removing the item, place it in a clothes dryer set on low heat or no heat, and allow the item to tumble until dry. Brush with clean suede brush after removing from dryer. NOTE OF CAUTION, be careful about washing suede Jackets or Vests that have a lining, make note if the fabric is of the type that can be washed, if the lining shrinks it may have to be removed.
HOW TO RESTORE ROUGH OUT- SUEDE LEATHER CHAPS
Light colored chaps that have become very ugly from use, can have a totally new life if cleaned & dyed a darker color. The method above for washing works awesome for commercial tanned suede, show chaps. If Rough-Out or Suede Chaps become dingy or faded, place them in the washer with a bottle of colored Rit dye for dying fabric, set the water level to small load, run the wash cycle two times with the dye in the water, don't allow the washer to go into the rinse cycle until after completing two wash cycles with the Rit dye, then add fabric softener in the rinse cycle, use the same method for drying as above, tumble dry low heat, brush to perk up after the chaps are dry. NOTE... remove all Silver Conchos & etc if they might become damaged in the process of cleaning or drying the chaps. If you can't remove the buckles & etc. place the chaps in a cloth bag, such as a pillow case, tie it closed and dry the chaps this way.