I certainly don''t know of any good way to wash clothes aboard; but we used a good book, a bucket and a toilet plunger.
1. a little soapy water in the bucket.
2. Cothes in bucket
3. Agitate cothes /w plunger.
4. Read book while doing so.
5. Empty bucket & squeeze clothes dry.
6. Fresh water & clothes in bucket.
7. Reapeat 1 thru'' 4 as required.