Ultrasonic.. probably way I will go since have 1000w solar
Should be great for stains, sweet marks etc. and may reduce need to wash whole item but once a month if you also stiff brush rest of item to remove skin cells etc.
. bucket and vibes- various forms of these.... basically you put cloths items in a bucket of water and agitate the cloths with a larger ultrasonic emitter. IMHO guess... get like 3 inexpensive ones to maximize the setup.