You can also wash stuff in a sink if you don't get caught...I don't know if it actually makes the clothes cleaner, but it helps with the smell. Which is really the only problem with the clothes in the first place right?
Just threw a bar of soap & whatever suspect article of clothing into the sink, work up a good lather and you're set! Rinse off with warm or cold water and hang out to dry.
Just beware hostel owners HATE it when people do this...so watch out.