The concept of sinkwashing only your underclothing has merit if your trip is not during warm weather. You can in fact rely on natural fiber clothing which can be aired out and worn a few times unless it is really soiled. The problem - unless you have lightweight wool or linen - is weight. Cotton clothing is heavy. For warm weather, packing enough cotton clothing to wear a fresh outfit every day makes for a very heavy and bulky load. You may be able to rely on hotel or coin laundry depending on where and how you travel. But beware: I’ve been on 10-day trips in Europe where not one of five or six hotels had laundry service of any kind.