You could thread baste it to muslin (or an old sheet, if the sheet is easy to needle) and then handwash inside a sheet cradle in the bathtub (which I think is described in the other thread). Basting it a sheet first would help keep stress off the joining threads. Do be sure to use lots and lots of water, though, to dilute any dyes that may bleed at first. You want to keep any loose dyes diluted as much as possible so they don't settle into other fabrics.