When I lived in Germany and I was traveling, I always took a tube of Rei in der Tube (Rei.i.d.T.) detergent with me for hand washing in hotels. The tube itself is lightweight, the product is fantastic, and it lasts a good long while because it doesn't take much to clean a couple of articles of clothing.
Rei.i.d.T. is a pH-neutral detergent with a consistency similar to that of toothpaste. And it works, really works--ask any musician who has played a concert and sweated like they had just run a marathon: Rei.i.d.T. will take out even the rather unattractive stench of sweat-soaked polyester.
Rei.i.d.T. is available not only in Germany (at pretty much every grocery or drug store), but also available from the German Deli in Texas. There is a minimum order requirement of $25, so I'd suggest getting a tube for a friend or two, and maybe some of those delicious German gummy bears to take with you on your next trip.
Before you take off, be sure to pick up a universal drain stopper at the grocery store; it costs just a buck or two, packs flat, and is infinitely helpful in any sink or bathtub where the drain doesn't close properly. A thin rope or travel clothes line is also helpful. I've used the same, thin boating rope for years and there are almost always two points to tie it to in a hotel room to dry lighter items. (Heavier items I hang over the towel rack in the bathroom, a natural humidifying process that helps immensely in dry hotel rooms.) 6-8 plastic clothespins have done the trick for me for years and I keep it all together in a self-sealing plastic bag with a travel-sized lint roller. It's become a travel essential for me; so much so that I call it my 'travel pack.'
Off you go on your next adventure!