A friend and I just returned from a trip to Japan, and what we learned along way can easily be translated to European travel. I used a XL Ziploc bag as a clothes washer, and it worked wonderfully! Just put in the clothes, add the soap and water (I had individual packets of Tide for sink washing), close the bag and agitate. It got everything WAY cleaner than just washing in a sink, and it made rinsing equally easy. When it was time to come home, I purchased about a dozen bottles of Japanese soda to bring home to friends, so I just put all the bottles inside the Ziploc bag to prevent leakage in case any of them came open during the flight. The bag folded down very small and was packed into an interior pocket, so it only took up room that would have otherwise been empty!
Seems like a good idea! I might do this is a backup. I will have to do laundry probably 2-3 times while over there and most areas I will be in will have easy access to a laundry room.