All recommendations are to brush it and if needed then clean it further with mild soap on a cloth, rinse and dry in the sun. The Acorn bags are made from waxed canvas and a washing maching would not be kind to them.

You may want to put a preservative on the leather straps, maybe some Proofide if you have a Brooks saddle?

My Acorn bag looked a little sketchy, but a good brushing and vacuum job and it looks good now - not new but cared for, which fits in nicely with C&V.