I recommend a so-called archival washer or slot washers with up to six sealed compartments. They get too heavy if they have too many compartments. They are usually made out of plexiglass and unfortunately very expensive. Tub washers have the disadvantage that the last unwashed print is always contaminating the already washed or half-washed prints, unless all prints are washed at the same time. Tray washing works just as well as archival washers, but it is not very efficient if more than a few prints have to be washed.